ARTICLE IN PRESS

0967-0645/$ - se

doi:10.1016/j.ds

�CorrespondE-mail addr

bkoch@awi-bre

Deep-Sea Research II 55 (2008) 988–999

www.elsevier.com/locate/dsr2

Stratification and the distribution of phytoplankton, nutrients,inorganic carbon, and sulfur in the surface waters of Weddell Sea leads

H.J. Zemmelinka,b,�, L. Houghtonc, J.W.H. Daceyc, J. Stefelsd, B.P. Koche,M. Schrodere, A. Wisotzkie, A. Scheltzf, D.N. Thomasg, S. Papadimitrioug,

H. Kennedyg, H. Kuosah, T. Dittmari

aRoyal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg, The NetherlandsbUniversity of East Anglia, NR9 7TJ Norwich, UK

cWoods Hole Oceanographic Institution, Woods Hole, MA 02543, USAdLaboratory of Plant Physiology, University of Groningen, 9750 AA Haren, The Netherlands

eAlfred Wegener Institute for Polar and Marine Research, Bussestr. 24, 27570 Bremerhaven, GermanyfInst. f. Polarokologie,Wischhofstr. 1-3, Gebaude 12, D-24148 Kiel, Germany

gCollege of Natural Sciences, Bangor University, Anglesey, UKhTvarminne Zoological Station, FI-10900 Hanko, Finland

iDepartment of Oceanography, Florida State University, OSB 311, Tallahassee, FL 32306-4320, USA

Accepted 23 December 2007

Available online 12 March 2008

Abstract

The distribution (fine resolution depth profiles) of major nutrients, chlorophyll-a, organic compounds, and phytoplankton (biomass

and numbers) was examined in lead water in pack ice of the Weddell Sea. Samples were taken by pulling water into a syringe from a series

of depths from 0.002 to 4m. While concentrations of compounds of interest remained constant in the water column, an enhanced

depletion of nutrients (ammonium, nitrate, silicate, and inorganic carbon) occurred above the pycnocline at 0.1m. Coinciding with this

depletion was an increase of organic matter and chlorophyll. The change in carbon isotopic composition showed that an enhanced

primary production occurred at the sea surface. Cell counts and nutrient disappearance ratios suggest that primary production was

dominated by diatoms. These results show that the sea surface can have different chemical characteristics than the deeper water column.

r 2008 Elsevier Ltd. All rights reserved.

Keywords: Stratification; Phytoplankton; Nutrients; Inorganic carbon; Sulfur compounds; Southern Ocean

1. Introduction

Sea-ice formation is an important characteristic of bothpolar regions, which at its maximum extent covers 6% ofthe Earth’s surface (Gloersen et al., 1992). In the SouthernOcean, the annual extent of sea ice ranges from a minimumof 4� 106 km2 in summer to a maximum of 19� 106 km2 inwinter and forms one of the largest biomes on Earth. Sea-ice research over the past decades has improved ourunderstanding of many of the physical processes thattransform surface waters into a matrix of ice and liquid.

e front matter r 2008 Elsevier Ltd. All rights reserved.

r2.2007.12.011

ing author. Tel.: +31222 369 438; fax: +31 222 319 674.

esses: henkz@nioz.nl (H.J. Zemmelink),

merhaven.de (B.P. Koch).

Sea ice is constantly in motion driven by the wind. Windstress drives the sea ice through frictional drag that createsa divergent stress over large areas of ice. Since ice has littlestrength under tension, this divergence can open up cracksthat widen to form leads. The surface area of leads variesday-to-day by refreezing and with the cyclical periods ofdivergence and convergence caused by the wind. However,sea-ice leads are highly important for the energy flux, in theform of heat, to the atmosphere (Eisen and Kottmeier,2000). In addition, the sea-ice habitat appears to be highlyproductive during spring and summer and is thought tomake a major contribution to global sulfur and carboncycling (Trevena et al., 2003; Semiletov et al., 2004;Zemmelink et al., 2005a, b, 2006a, b). Estimation of the

ARTICLE IN PRESS

Salinity (‰)

Dep

th (m

)

0

1

2

3

4

527 28 29 30 31 32 33 34 35

Fig. 1. Vertical profiles of salinity. The K represent the well-mixed water

column, J are data from the stratified water column.

H.J. Zemmelink et al. / Deep-Sea Research II 55 (2008) 988–999 989

annual productivity of the sea-ice flora remains incon-clusive, although it is generally accepted that Antarctic seaice sustains a significant uptake of atmospheric CO2,ranging from 0.015 to 0.024 Pg C in spring and summer(Delille, 2006). Zemmelink et al. (2006a, b) estimated fromdirect CO2 flux measurements that the total carbon uptakeby the multi-year-ice zone of the western Weddell Seain December 2004 could have been as high as 6.6 Tg C.However, part of the CO2 fixed by sea-ice algae may beremineralized and made to enter the surface sea waterinorganic carbon pool and/or be ultimately returned to theatmosphere during the annual cycle of exchange ofmaterials and organisms between the ice and the watercolumn.

In recent years, the high productivity of surface sea-iceassemblages, as well as assemblages in brine channels andgap layers, has been well documented (e.g., Thomas andDieckmann, 2003, and references therein). For sea-ice algalcommunities transport through brine channels and gaplayers is fundamental to nutrient replenishment (Goldenet al., 1998). In addition, increase in ice porosity, as sea-icewarms up, may facilitate exchange of nutrients and biotawith the water column. Melting sea ice will impact localand regional physical, chemical, and biological oceano-graphic processes. Low-salinity and low-density melt waterfloats on top of the higher-density seawater, forming arelatively stable surface layer (Mitchell and Holm-Hansen,1991), unless disturbed by strong winds (Lancelot et al.,1991). During melting, solutes and particles within sea ice,including nutrients and sea-ice algae, are released to theupper water column. Phytoplankton blooms are commonlyassociated with the retreating sea-ice edge and polynyasand are a considerable portion of polar productivity (Smithand Nelson, 1986; Lancelot et al., 1993a, b; Schloss andEstrada, 1994; Smith and Gordon, 1997; Arrigo, 1998).

In order to study sea surface characteristics, Zemmelinket al. (2005a, b) developed a system for sampling biota,nutrients, and major sulfur compounds in Weddell Seaopen leads in the sea ice. First results from its applicationat the 2004 Ice Station POLarstern (ISPOL) cruise havebeen published recently by Zemmelink et al. (2005a, b) andshow that the chemical characteristics (salinity and majorsulfur compounds) of the near-surface seawater in WeddellSea leads are very different from the underlying watercolumn during periods of strong stratification caused by adecrease in salinity (see also Fig. 1). However, it was notclear whether the observed gradients were the result ofphysical and/or biological process, a question that can onlybe addressed using a more comprehensive data set. In thispaper, we present depth profiles of the concentration ofmajor nutrients (dissolved inorganic phosphorus (DIP),silicic acid, nitrate plus nitrite, and dissolved ammonium),dissolved organic nitrogen (DON), dissolved organiccarbon (DOC), dissolved inorganic carbon and its stableisotope ratio (DIC and d13C-DIC, respectively), as well aschlorophyll and the major sulfur compounds (dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP) and

dimethylsulfoxide (DMSO)) in the water column of leadsfrom 0.002 to 4m depth. This paper gives a firstcharacterization of the chemical characteristics of thenear-surface water column, in open leads in the perennialice zone of the western Weddell Sea.

2. Materials and methods

2.1. Sampling

Seawater was sampled from two leads adjacent to theISPOL ice floe. Lead 1 was newly opened and was sampledfrom day 350 to 359. Lead 2 was 2 weeks old whensampling started from days 362 to 001. Sampling occurredbetween 12:00 and 16:00 GMT and started after a period ofelevated wind speeds during which waves mixed the upperwater column. Samples in lead 1 were taken from 0.002,0.25, 1, and 4m water depth. Lead 2 was also sampled at0.1m depth. It is noted that we define a depth of 0.002m assurface water, although we realize that the sample is drawnfrom a sphere around the sampling tube inlet. Sampleswere taken by suspending 0.001m (internal diameter)Teflon sampling inlets from a small catamaran and bypulling water into a 50-mL syringe at a speed of5mLmin�1. Sample collection at different withdrawalspeeds (2, 5, and 50mLmin�1) and with different syringes(glass and plastic) showed no significant effect on theconcentration of sulfur compounds (n ¼ 20, po0.05). Itcan therefore be assumed that this sampling method doesnot affect other parameters of interest. Sampling inlets andsyringes were rinsed three times before water was collectedinto vials for later analysis of compounds of interest.Samples were taken in a specific order to minimizesampling artifacts: first samples were drawn for sulfurcompounds (0.5–1L), second phytoplankton (0.02 L), thirdnutrients (0.8 L), fourth chlorophyll (1 L), and fifth salinity

ARTICLE IN PRESSH.J. Zemmelink et al. / Deep-Sea Research II 55 (2008) 988–999990

(0.15 L). In total, about 2.5 L water were taken from closeto the surface and 3L from 1 and 4m depth.

2.2. Analytical methods

The analysis of salinity and major sulfur compounds(DMS, total DMSP, and total DMSO) was presented indetail in Zemmelink et al. (2005a, b). All samples used inmicroscopy were fixed with ice-cold 25% EM-gradeglutaraldehyde solution (final conc. about 1%) immedi-ately after sampling. Duplicate 5-mL samples were filteredonto black Nuclepore polycarbonate filters (pore-size0.2 mm) after staining them with proflavine (Haas, 1982).In total, 100 mL of proflavine solution (0.033% W/V) per5-mL sample was added and gentle filtration (o5 kPavacuum) was started without delay. Immediately after thefiltration was completed the vacuum was stopped, and thefilter air-dried and mounted in paraffin oil to a glass slide.The samples were examined and counted within 24 h, andthe samples kept in +4 1C before counting.

All counts were made with a Leitz Dialux microscopeequipped with epifluorescence light. A 50-W HBO mercurylamp and the Leitz Ploemopak filter set I2 were used. Thefilter set gives blue light, with which proflavine-stained cellswere seen as green, and chloroplasts as red bodies insidecells. Nucleus is usually clearly visible as a green body. Allcells except individual Phaeocystis were counted from thewhole filter area with a 40� objective. Phaeocystis cellswere enumerated from either one or two transects coveringthe whole diameter of the filter. Diatom cells withoutchloroplasts and nucleus were considered dead, and notincluded to counts. As the epifluorescence microscopy israrely suitable for species identification, some samples wereexamined with a 100� oil immersion objective withnormal light. However, the species identification was stilllimited. About 50 cells of the most important taxa weremeasured from a selected sample to get its measures. Fromthe results mean individual cell volumes were calculated.

Onboard analyses for the major dissolved inorganicnutrients, nitrate plus nitrite (hereafter, nitrate (NO3

�)),DIP, and silicic acid were done using standard calorimetricmethodology (Grasshoff et al., 1983) as adapted for flowinjection analysis (FIA) on a LACHAT InstrumentsQuick-Chem 8000 autoanalyzer (Hales et al., 2004).Dissolved ammonium (NH4

+) also was determined on-board with the fluorimetric method of Holmes et al. (1999)using a HITACHI F2000 fluorescence spectrophotometer.Samples for DON were filtered through syringe filters(Whatman GD/X GMF, pore size 0.45 mm) and were keptat �18 1C until later analysis. The DON was determined bysubtraction of NO3

� and NH4+ from the total dissolved

nitrogen analyzed by FIA on the LACHAT autoanalyzerusing on-line peroxodisulfate oxidation coupled with UVradiation at pH 9.0 and 100 1C (Kroon, 1993; Kattner andBecker, 1991).

Samples for DOC were filtered through precombusted(550 1C, 6 h) glass fiber filters (GF/F, Whatman) and stored

frozen at �30 1C until analysis. DOC in the filtrate wasdetermined by high-temperature catalytic oxidation with aShimadzu TOC-VCPN analyzer. In the autosampler, 6mLof sample volume were acidified with 0.12mL HCl (2M)and sparged with oxygen (100mLmin�1) for 5min toremove inorganic carbon. In total, 50 mL sample volumewas injected directly on the catalyst (heated to 720 1C).Detection of the generated CO2 was performed with aninfrared detector. Final DOC concentrations were averagevalues of triplicate measurements. If the standard variationor the coefficient of variation exceeded 0.1 mM or 2%,respectively, up to two additional analyses were performedand outliers were eliminated. Detection limit was 7 mM C,with an accuracy of 72 mM C determined with low carbonwater and seawater reference material (DOC-CRM,Hansell Research Lab, University of Miami, USA).The DIC samples were immediately filtered through a

cellulose nitrate filter (0.45 mm, Sartorius) into HgCl2-poisoned 10-mL glass ampoules, which were stored flame-sealed under a nitrogen atmosphere for analysis in thehome laboratory. The DIC concentration and d13C-DICwere determined following in-vacuo reaction with 85%H3PO4 and cryogenic CO2 gas distillation, using an in-linemanometer and a EUROPA PDZ 20/20 mass spectro-meter, respectively. The isotopic measurements are re-ported in the d notation relative to Vienna Pee DeeBelemnite, i.e., dsample ¼ 1000 [(Rsample/Rstandard)�1], whereR ¼ 13C/12C. The reproducibility of DIC and d13C-DICmeasurements based on internal seawater standard andduplicate sample measurements was better than5 mmol kg�1 and 0.1%, respectively.For chlorophyll-a (chl-a) determination each water

sample was filtered onto Whatman GF/F (Whatman plc.,Brentford, Middlesex, UK) glass microfiber filters andchl-a was extracted in 96% ethanol in the dark for 24 h atroom temperature. Fluorescence was measured using aJasco FP-750 fluorometer (Jasco Inc., Tokyo, Japan)calibrated against pure chl-a (Sigma–Aldrich Company,St. Louis, MO, USA) and the concentrations werecalculated according to Helcom (1988).

2.3. Data presentation

In order to remove the effect of dilution with freshwater(from ice melt) all variables are scaled to a constant salinityof 34.3% (as indicated by the subscript 34) using[A]34 ¼ [S]y*[A]y/34.3, where [S]y is the salinity at depth y

and [A]y the concentration of variable A at depth y. Inaddition, concentration changes over time are derived from([A]yd1�[A]yd2)y/([B]yd1�[B]yd2)y, where ([A]yd1�[A]yd2)y isthe concentration difference of variable A between yeardays 1 and 2 at depth y.

3. Results

A detailed discussion of environmental conditions,salinity, and sulfur profiles in the water column is given

ARTICLE IN PRESSH.J. Zemmelink et al. / Deep-Sea Research II 55 (2008) 988–999 991

by Zemmelink et al. (2005a, b). Briefly, water temperaturewas about �1.8 1C and wind speed varied between 3.6 and9.2m s�1. Aerial photography data revealed a number ofsignificant changes in the character of the pack ice between29 November 2004 and 1 January 2005. There was a netdecrease in the concentration of thick, snow-covered floesfrom 96% to 90%; however, this did not reflect a netdecrease in total ice concentration. Instead, we observed anincrease from 1% to 7% in the amount of brash ice betweenthe floes, much of which was brown due to the high diatomconcentrations and therefore highly productive. Thiscoincided with a net decrease in floe size, while the open-water fraction of leads averaged 5% throughout December.

The relative position, of the sample site, to the directionof the wind varied from down wind to up wind.Stratification was observed from year day 354 until 359in lead 1, and started in the second lead at year day 364,lasting until the end of our stay at the floe at year day 001.Salinity profiles are summarized in Fig. 1 and show that thewater column became less saline above a depth of 0.1m. Inthe mixed water column, the salinity was close to 34.3%(34.27%70.046; n ¼ 38, from 4m depth to close to thesurface). In calmer conditions, stratification occurred andsalinity at the surface dropped to a minimum of 27.4%.However, water samples taken at 0.25m and belowremained at salinity around 34.3% throughout themeasurement period. A similar stratification was observedin the biogeochemical parameters.

Overall very little algal biomass was found throughoutthe water column, with maxima only occurring at thesurface (Fig. 2). The distribution of phytoplanktonbiomass was variable and showed that single-celledPhaeocystis and autotrophic dinoflagellates were mostabundant at year days 352, 354, 358 (in lead 1) and atyear day 363 in lead 2. However, during most days withstratification (except year day 358) diatoms becamedominant in biomass at the surface. Diatom species weredominated by Fragilariopsis cylindrus and Cylindrotheca

closterium, which were both found to be dominant in icebottom and infiltration layer in the ISPOL ice floe. (Resultsof sea-ice algal compositions are presented elsewhere in thisspecial issue.) Other ice-related species were rare, and otherfound diatoms were mainly genuine centric planktonicdiatoms (Fig. 3).

Chl-a34 concentrations (Fig. 4, Table 1) in the mixedwater column of lead 1 averaged 0.1570.05 mgL�1

(n ¼ 16), increasing to 0.47 mgL�1 towards the surfaceduring stratification. In the second lead, chl-a34 concentra-tions increased from 0.1670.04 mgL�1 (n ¼ 17) in themixed column to 0.41 mgL�1 during stratification. Whilethese values are in the low range of the reportedchlorophyll concentrations in the Weddell Sea (e.g.,Kattner et al., 2004), the depth profiles clearly demonstratethe significant effect of stratification on the distribution ofchl-a in the water column.

A similar strong relationship was found between DOCand salinity but not for DON and salinity. The concentra-

tions of DOC34 (Fig. 4, Table 1) ranged from 40.5 to43.6 mM in the mixed water column of lead 1, increasing toa maximum of 49.0 mM near the surface during stratifica-tion. In the second lead, DOC34 values ranged from 41.3 to44.5 during mixed conditions, increasing to 57 mM abovethe pycnocline. These values are typical concentrations inAntarctic seawater (Wedborg et al., 1998). The DON34

concentration (Fig. 4, Table 1) was variable in the twoleads, ranging from 0.2 to 12.6 mM, with highest DONvalue of 12.6 mM at day 353. The DON distribution withdepth in lead 1 was similar to that of DOC, with increasingconcentrations towards the surface during stratification.The distribution of DON with depth in lead 2 did not showa relationship with salinity and, hence, a stratificationeffect. The measured DON concentrations were similar tothose previously measured in the water column of theWeddell Sea (Thomas et al., 2001).The measured concentration range of the major dis-

solved inorganic nutrients (Fig. 4, Table 1) in the mixedwater column is also typical of Weddell Sea water(Schroder et al., 1994; Thomas et al., 2001), with in lead1 nitrate34, silicic acid34, and DIP34 ranging from 19.7 to30.0 mM, 42.6 to 52.0 mM, and 1.81 to 3.81 mM, respec-tively. During stratification, the dissolved nutrient concen-trations in lead 1 decreased to 0.9 mM for NO3

�34, 8.8 mM for

Si34, and 0.06 for PO434. Concentrations in the second leadwere similar, with nitrate34 ranging from 24.4 to 30.9 mM,silicic acid34 ranging from 48.7 to 61.4 mM and DIP34

ranging from 2.1 to 2.6 mM, respectively. During stratifica-tion, the dissolved nutrient concentrations in lead 2decreased to 0.08 mM for NO3

�34, 18.4 mM for Si34, and 0.8

for PO434.The DIC and d13C-DIC (Fig. 4, Table 1) were measured

only in lead 2. Normalized DIC concentration was uniformin the mixed water column, averaging 229775.7 mM(n ¼ 14), decreasing at the water surface during stratifica-tion to 1223 and 1187 mM. The d13C-DIC34 was alsorelatively uniform in the mixed water column, with anaverage of 0.5970.12% (n ¼ 14). During stratification, thed13C-DIC in the surface layer increased (i.e., becameenriched in 13C) to +1.2% and +4.3%. The d13C-DICmeasurements are in agreement with previously reportedmeasurements in platelet ice layers (+0.4% to +3.8%;Thomas et al., 2001) and in under-ice seawater (�0.5% to�2.5%; Gibson et al., 1999).Although there is some overlap with DMS, DMSP, and

DMSO data presented in Zemmelink et al. (2005a, b), herewe present only data of (normalized) sulfur compoundsthat were collected simultaneously with samples used foranalysis of nutrients, chlorophyll and biota. (Hence, datapresented in this study differ from data presented inZemmelink et al., 2005a, b.) Major sulfur compoundsDMS34, DMSP34, and DMSO34 in the mixed water columnof lead 1 ranged from 0.3 to 5.3 nM, 3.4 to 19.2 nM, and2.2 to 16.0 nM, respectively. During stratification, thesulfur concentrations increased to 17.2 nM for DMS34,68.5 nM for DMSP34, and 80.2 nM for DMSO34. Similar

ARTICLE IN PRESS

Diatom biomass (l-1)

0

Dep

th (m

)0

1

2

3

4

5

351352354356358359

Diatom biomass (l-1)

0

Dep

th (m

)

0

1

2

3

4

5

363364365366001

Non diatoms biomass (l-1)

0.0

Dep

th (m

)

0

1

2

3

4

5

Non diatoms biomass (l-1)

0

Dep

th (m

)0

1

2

3

4

5

Total biomass (l-1)

Dep

th (m

)

0

1

2

3

4

5

Total biomass (l-1)

0

Dep

th (m

)

0

1

2

3

4

5

Lead 1 Lead 2

2e+6 4e+6 6e+6 8e+6 1e+7

5.0e+6 1.0e+7 1.5e+7 2.0e+7 2.5e+7

0.0 5.0e+6 1.0e+7 1.5e+7 2.0e+7 2.5e+7 1e+6 2e+6 3e+6 4e+6 5e+6 6e+6

2e+5 4e+5 6e+5 8e+5

1e+6

1e+6

2e+6 3e+6 4e+6 5e+6

Fig. 2. Algal biomass in plasma volume (109 mm3L�1). Graphs in the left column are based on lead 1; graphs to the right are based on lead 2.

H.J. Zemmelink et al. / Deep-Sea Research II 55 (2008) 988–999992

ARTICLE IN PRESS

Other diatoms (cell number l-1)

0

Dep

th (m

)

0

1

2

3

4

5040 80 120 5 10 15 20 25

Phaeocystis (cell number l-1)

0

Dep

th (m

)

0

1

2

3

4

50

351352354356358359

363364365366001

Dinoflagellates (cell number l-1)

0

Dep

th (m

)

0

1

2

3

4

50

Fragilariopsis cylindrus (cell number l-1)

0

Dep

th (m

)

0

1

2

3

4

50

Cylindrotheca closterium (cell number l-1)

0

Dep

th (m

)

0

1

2

3

4

50

Lead 1Lead 2

3000 6000 100 200 300

1000 2000 5 10 15 20 200 400 200 400

10 20 30 40 2 4 6 8 10

Fig. 3. Abundance (cell number l�1) of major phytoplankton groups. Graphs on the left site are based on lead 1 and graphs on the right are based on

lead 2.

H.J. Zemmelink et al. / Deep-Sea Research II 55 (2008) 988–999 993

concentrations were measured in lead 2 with DMS34 in themixed column ranging from 0.63 to 3.1 nM, DMSP34

concentrations ranging from 8.2 to 26.7 nM, and DMSO34

ranging from 2.1 to 12.7. In comparison with lead 1 slightlyhigher concentrations were measured above the pycnoclineof lead 2 with sulfur concentrations increasing to values ashigh as 38.2 nM for DMS34, 70.5 nM for DMSP34, and158.9 nM for DMSO34 (Fig. 5 and Table 1).

4. Discussion

In both leads, the water column appeared to be wellmixed at the first sampling days (year days 353 and 363,respectively), which was caused by the elevated windspeed and the occurrence of short breaking waves duringthe preceding days. No profiles were observed duringsuch conditions but stratification rapidly occurred, and

ARTICLE IN PRESS

Chl-a34 (mg l-1)

0.0

Dep

th (m

)0

1

2

3

4

5

Chl-a34 (mg l-1) DOC34 (μM)

40

DOC34 (μM)

40

DON34 (μM)0

Dep

th (m

)

0

1

2

3

4

5

DON34 (μM) NOx34 (μM)0

NOx34 (μM)

Si34 (μM)10

Dep

th (m

)

0

1

2

3

4

5

Si34 (μM) DIP34 (μM)0

DIP34 (μM)1

DIC34

Dep

th (m

)

800

0

1

2

3

4

5

δ13CDIC34

0

Lead 1Lead 2

0.2 0.4 0.6 0.2 0.4 0.6 45 50 55 60 45 50 55 60

2 4 6 8 10 12 14 2 4 6 8 10 12 14 10 20 30 40 10 20 30 40

20 30 40 50 60 70 20 30 40 50 60 70 1 2 3 4 2 3 4

1200 1600 2000 2400 1 2 3 4 5

Fig. 4. Vertical profiles from 0.002 to 4m depth of particulate and dissolved constituents in Weddell Sea leads. All data are normalized to a salinity of

34.3%. Symbols refer to sampling dates, presented as year day. Graphs on the left site are based on lead 1 and graphs on the right are based on lead 2. DIC

data are derived from lead 2 only.

H.J. Zemmelink et al. / Deep-Sea Research II 55 (2008) 988–999994

ARTICLE IN PRESS

Table 1

Biochemical parameters measured in sea-ice leads during the ISPOL experiment

Parameter Stratified water column above pycnocline Mixed water column

Lead 1 Lead 2 Lead 1 Lead 2

Salinity (%) 30.27 (28.65–32.6) 28.03 (27.35–28.25) 34.26 (24.28–34.35) 34.28 (34.07–34.31)

Chl-a (mgL�1) 0.35 (0.33–0.47) 0.36 (0.3–0.41) 0.15 (0.07–0.23) 0.16 (0.07–0.21)

DoC (mM) 48.6 (47.9–49.0) 57 N.A. 42.0 (40.5–43.6) 42.7 (41.3–44.5)

DoN (mM) 5.2 (3.8–7.0) 2.0 (1.4–2.6) 4.4 (0.2–12.6) 2.1 (0.5–5.2)

NO3�(mM) 4.9 (0.9–11.6) 11.4 (6.1–20.8) 26.3 (19.7–30.0) 27.5 (24.4–30.9)

NHx (mM) 0.44 (0.16–0.59) 0.33 (0.08–0.61) 0.64 (0.14–1.78) 0.27 (0.05–0.65)

Si (mM) 18.6 (8.8–36.3) 26.6 (18.4–42.8) 48.4 (42.6–52.0) 54.1 (48.7–61.4)

DIP (mM) 0.4 (0.06–1.0) 1.2 (0.8–2.0) 2.3 (1.81–3.81) 2.4 (2.1–2.6)

DIC (mM) 1411 (1187–1823) 2297 (2292–2308)

d13CDIC (%) 1.9 (0.4–4.3) 0.59 (0.37–0.79)

DMS 8.7 (3.1–17.9) 29.0 (13.4–38.2) 1.1 (0.3–5.3) 1.4 (0.63–3.1)

DMSP 66 (53.0–68.5) 57.9 (21.3–70.5) 10.0 (3.4–19.2) 17.4 (8.2–26.7)

DMSO 34.5 (13.3–80.2) 88.8 (10.0–158.9) 7.6 (2.2–16.0) 7.6 (2.1–12.7)

DSi:DN lead 1 2.0 2.6

DSi:DN lead 2

DN:DP lead 1 9.2 8.4

DN:DP lead 2

DC:DP lead 2 740 49

DC:DN lead 2

DMSP chl-a (nM mg�1) 189 (n ¼ 4) 161 (n ¼ 3) 67 (n ¼ 16) 106 (n ¼ 17)

DMSP:DMS 7.6 (n ¼ 4) 2.0 (n ¼ 3) 8.8 (n ¼ 16) 12.4 (n ¼ 17)

DMS:DMSO 0.24 (n ¼ 4) 0.33 (n ¼ 3) 0.15 (n ¼ 16) 0.19 (n ¼ 17)

Presented are average values and, between parentheses, minimum and maximum values. All presented data are normalized to a salinity of 34.3%. Ratios

(DA:DB) are calculated from the change between concentrations found at the sea surface during mixed conditions and minimal concentrations found

during stratification. Sulfur ratios are based on the average values found in the respective water column.

H.J. Zemmelink et al. / Deep-Sea Research II 55 (2008) 988–999 995

enhanced with time, when breaking waves were notpresent. During stratification concentrations of chemicalcompounds changed at the surface (as sampled at 0.002mdepth), probably initialized by processes such as dilutionwith melt water and biological activity.

Nutrients behave conservatively during freezing andmelting of seawater, and, if this were the only processaffecting their concentration, salinity normalization wouldbring them close to the respective seawater measurementsin the mixed layer. However, salinity corrected concentra-tions of nutrients appear to be substantially depleted abovethe pycnocline (Fig. 4). It is therefore unlikely that dilutionfully determined the disappearance of nutrients.

The biological consumption of nutrients can be deter-mined from uptake ratios (Table 1) derived from theconcentration changes from the onset of stratification (yeardays 353 and 363) till the last sampling day (year days 359and 001, respectively). In addition, the ratio can be used asan indication of which plankton species is most abundant.Because diatoms use large quantities of silicate to formtheir opal tests, the ratio of changes in silicate and nitrateconcentrations, DSi34/DN34, can be used as an indicationof diatom over Phaeocystis dominance. The maximumDSi34/DN34 ratio of concentration change in the surfacewaters of the two leads was 2.0 and 2.6 (Table 1), which,following Sweeney et al. (2000), indicates diatom dom-inance. Values less than 0.5 for the DSi34/DN34 ratio would

indicate a Phaeocystis dominated algal community. Inaddition, some studies have identified diatoms as thesource of low N/P and C/P removal ratios (Arrigo et al.,1999; Sweeney et al., 2000), whereas N/P uptake ratios inPhaeocystis-dominated communities exceed the Redfieldratio (N:P ¼ 16). The observed DNOx34:DDIP34 in lead 1of 9.2, and in the second lead DNOx34:DDIP34 of 8.4, bothlower than the Redfield ratio (N:P ¼ 16), indicate adominance of diatoms above the pycnocline of both leads.This is consistent with the general observation thatphytoplankton blooms are dominated by Phaeocystis inrelatively unstratified waters, while in stratified surfacewaters blooms are dominated by diatoms (Arrigo, 1998;Arrigo et al., 2000).Consistent with the distribution of macronutrients,

concentrations of DIC34 dropped considerably betweenyear days 363 and 001 by 1068 mM. The progress of NO3

�

and DIP deficit with DIC deficit indicates the evolutionof strong nutrient gradients in the surface water abovethe pycnocline with removal ratios DC34:DNO3

�34 and

DC34:DP34 in lead 2 increasing to 49 and 740, respectively.While the DNO3

�:DPO4 ratios during ISPOL are commonfor diatom-dominated waters, the overall DC:DN:DP ishigh. Although the number of observations presented hereis small, these numbers are in agreement with resultspublished by Gleitz et al. (1996). Results show a strongdrawdown of DIC that coincides the drawdown of major

ARTICLE IN PRESS

DMSP34 (nM)0

Dep

th (m

)

0

1

2

3

4

5

DMSO34 (nM)0

Dep

th (m

)

0

1

2

3

4

5

DMS34 (nM)0

Dep

th (m

)

0

1

2

3

4

5

Lead

5 10 15 20

20 40 60 80 100

20 40 60 80 100 120

DMSP34 (nM)0

DMSO34 (nM)0

DMS34 (nM)0

Lead

50 100 150 200

20 40 60 80 100

10 20 30 40 50

Fig. 5. DMS, (total) DMSP, and (total) DMSO (nM) from 0.002 to 4m depth in the water column of Antarctic leads. All data are normalized to a salinity

of 34.3%. Symbols refer to sampling dates, presented as year day. Graphs in the left column are based on lead 1, graphs to the right are based on lead 2.

H.J. Zemmelink et al. / Deep-Sea Research II 55 (2008) 988–999996

nutrients. Such a drawdown of nutrients can be expected ina closed or semi-closed environment, where nutrientreplenishment (including DIC) during stratification fromthe mixed layer below the sea surface, or other sources(e.g., ice, atmosphere), is slow relative to the time ofobservation. Replenishment of the DIC pool in thestratified water column from the atmosphere by CO2 gasexchange was likely limited by diffusion-controlled trans-port processes under conditions of lack of turbulence at the

air–water interface, at least on the short time-scale of thepresent study. Enhancement of this transport by chemicalreaction of atmospheric CO2 with OH� at elevatedpH, such as expected during intense photosyntheticevents in a semi-closed system, is a possibility. However,chemical enhancement of CO2 transport across the air–seainterface is associated with faster kinetics of incorporationof 12CO2 than

13CO2 into the DIC pool of surface waters.Such strong depletion of 13C in the DIC pool is not

ARTICLE IN PRESSH.J. Zemmelink et al. / Deep-Sea Research II 55 (2008) 988–999 997

supported by the current, albeit limited, number of isotopicmeasurements.

Similar microenvironments have been described in watercolumns of crack pools trapped between melting ice floes(Gleitz et al., 1996). The crack pools displayed NO3

�

exhaustion and were thought to have evolved due to rapidalgal growth from an initially nutrient-rich and high-salinity pool. The observed nitrate exhaustion was usuallyassociated with a significant rise in pH values from 8.3 to9.2. Gleitz et al. (1996) estimated that the rise by onepH unit would require a decrease of 7700 mM DIC,equivalent to the DIC decrease (of 764 mM, uncorrected forsalinity) observed at the surface of the lead 2 duringstratification.

Nutrients together with light play a major role indetermining the distribution and magnitude of phyto-plankton biomass and primary production. There are a fewlikely explanations as to why Phaeocystis in unstratifiedwaters dominate while diatoms dominate in more stratifiedwater columns (as discussed by Arrigo, 1998). Theassimilation rate and photosynthetic efficiency of Antarcticdiatoms are only 20–50% that of Phaeocystis (Tilzer et al.,1986), making them less competitive in a highly dynamiclight environment of the turbulent water column. Phaeo-

cystis exhibits both high assimilation rates and highphotosynthetic efficiencies (Palmisano et al., 1986), distinctadvantages in an unstable water column where light levelsare changing rapidly (Richardson et al., 1983). In addition,the mucilaginous envelope surrounding Phaeocystis colo-nies is neutrally buoyant, allowing the colonies to remainnear the surface in a mixed water column. However, it canbe speculated that the mucus envelope makes Phaeocystis

subject to diffusion-controlled CO2 uptake and that suchcolonies are in fact CO2 limited. This would become evenmore profound in an environment where a strong draw-down of DIC occurs, as was observed above the pycnoclinein lead 2 during stratification. This could give diatoms acompetitive advantage over Phaeocystis at the onset ofblooms. In addition, as the onset of blooms is triggered bystratification driven by ice melt, the diatom dominance insea ice (as found at the ISPOL floe but also in other studies,Thomas and Dieckmann, 2002; Lizotte, 2003) mightoutcompete Phaeocystis when diatoms are introduced inlarge numbers into surface waters by sea-ice melting (Smithand Nelson, 1986).

Release from sea ice into the stratified surface watercolumn suddenly exposes phytoplankton to strong irra-diance, causing significant DNA damage that is likely toreduce community growth but also loss of biomass fromthe water column (Buma et al., 2001). The suddenenhancement of irradiance will require regulation andacclimation of light harvesting, photosynthesis, andphotoprotection. The transition from low to excessiveirradiance can over-reduce photosynthetic electron trans-port and initiate formation of reactive oxygen species.Sensitivity to excessive irradiance is strongly influenced byphotoacclimation and nutrient availability because these

conditions influence cellular pigment composition andprotein turnover rates (van de Poll et al., 2005).Oxidative stress caused by factors such as ultraviolet

radiation, low Fe and CO2 availability limit growth rateand can promote DMSP production (Sunda et al., 2002).In addition, in some cases, an increase of the release ofDMS by some Phytoplankton species was observed (Sundaet al., 2002). These factors, along with N limitation, lowtemperatures, and high PAR, are all known as oxidativestress factors in plants (Winston, 1990). Sunda et al. (2002)therefore suggested that DMSP may be part of an anti-oxidant system in marine phytoplankton. To support thishypothesis, they presented evidence that DMSP and itsknown degradation products (DMS, DMSO, and acrylate)could be effective scavengers of highly toxic OH� radicals.Since DMS is one of the most effective scavengers ofreactive oxygen species known (about 60� better thanDMSP), Sunda et al. further postulated that DMSPconversion to DMS via lyase activity might be inducedby oxidative stress.

Phaeocystis but also sea-ice diatoms are associated withhigh concentrations of DMSP and DMS (DiTullio et al.,1998; Trevena et al., 2003). The ability to use an effectiveradical scavenger system might explain why they are thedominant phytoplankton species in sea ice and along theretreating sea-ice edge. A profound increase of major sulfurcompounds, coinciding with a rise of chl-a concentrations,was found towards the surface of the stratified watercolumn. In the leads, the ratio between DMSP34 andchl-a34 increased from 67 nM mg�1 in the water column to189 nM mg�1 above the pycnocline of lead 1. In lead, twoDMSP34:chl-a34 ratios increased from 109 nM mg�1 in thewater column to 161 nM mg�1 at the surface in the stratifiedwater column (Table 1). In addition, the ratio betweenDMSP34 and DMS34 decreases by a factor two from themixed water column towards the surface in the stratifiedwater column of lead 2 (Table 1). From these ratios, thepossibility can be inferred that DMSP production andconversion to DMS increase as a reaction to oxidativestress at the sea surface.Although the increase of DMSP and chl-a are strongly

correlated, it cannot be concluded that high DMSP andDMS concentrations found at the surface are a result fromin-situ production alone and thus form an active protectionmechanism against oxidative stress. Sea ice could still be asource of these compounds. Trevena and Jones (2006)concluded that the source of elevated DMS and DMSPvalues in the water column of the Antarctic Sea ice Zonewas sea ice because chl-a concentrations in the watercolumn remained low.Photolysis is an important removal pathway for DMS

(Hatton et al., 2004). By pooling data from differentoceanic regions Hatton et al. (2004) found a highlysignificant correlation between DMS and DMSO in(near-)surface waters. The near-surface DMS and DMSOconcentrations do confirm this close correlation, but alsoshow that the ratio of DMS to DMSO (Table 1) increases

ARTICLE IN PRESSH.J. Zemmelink et al. / Deep-Sea Research II 55 (2008) 988–999998

from the mixed water column to the surface. This impliesthat DMS photolysis does not always result in DMSOproduction (as found in other studies, e.g., Kieber et al.,1996; Hatton, 2002), or that conversion pathways are ofdifferent importance at different depths of the stratifiedwater column. For example, the light regime at the surfacecould well inhibit the activity of bacteria at the surface andindirectly affect conversion pathways and rates of sulfurcompounds. Unfortunately, the ultimate cause of thedecreased DMS:DMSO ratios and the significance ofoxidative stress on the conversion and removal pathwaysof the major sulfur compounds in the surface waters cannotbe assessed from the present study.

The short field campaign in which this study took place bydefault only results in a brief ‘‘snap-shot’’ of the biogeo-chemistry of Weddell Sea leads. Concentrations of inorganicand organic compounds were found to be typical forSouthern Ocean waters. However, a distinct, but notextreme, different chemical environment develops abovethe pycnocline during meltwater-driven stratification events.During these events, the lead surface was enriched in organiccompounds and depleted in major nutrients. However, theorigin of the chemical gradients observed towards the seasurface is not straightforward. Water in the newly formedleads will largely be a mixture of seawater and meltwaterfrom the surrounding ice floes. Stratification occurs fairlyrapidly and traps the biological community at the surface ina habitat that is dominated by strong gradients in light andsalinity that slows down solute and particle exchange withthe deeper water column. The succession of sea-ice biota inthe surface layer is proposed to be comparable to a batchculture-type development (Gleitz et al., 1996). On short time-scales, equivalent to the period of observation in this study,the water surface above the pycnocline can be seen as anideal mesocosm to test hypotheses related to primaryproduction and adaptation to oxidative stress in the highradiation environment of the polar regions.

Acknowledgments

This work was financially supported by the Marie CurieTraining Site Fellowship (contract number HPMF-CT-2002-01865) and by NERC (Award Ref. No. NER/B/S/2003/00844). We would like to thank the WHOI OceanLife Institute. We would also like to thank D. Janssen(AWI), who performed the DOC analysis. The authorswould like to express their deepest thanks and appreciationto the crew of the R.V. Polarstern for all their efforts inhelping us throughout ANT XXII/2. Thanks also to thechief scientist Dr. M Spindler and to the AWI for makingthe cruise possible.

References

Arrigo Jr., K.R., 1998. Physical forcing of phytoplankton dynamics in the

southwestern Ross Sea. Journal of Geophysical Research 103,

1007–1022.

Arrigo, K.R., Worthen, D.L., Robinson, D.H., Dunbar, R.B., DiTullio,

G.R., VanWoert, M., Lizotte, M.P., 1999. Phytoplankton community

structure and the drawdown of nutrients and CO2 in the Southern

Ocean. Science 283, 365–367.

Arrigo, K.R., DiTullio, G.R., Dunbar, R.B., Lizotte, M.P., Robinson,

D.H., VanWoert, M., Worthen, D.L., 2000. Phytoplankton taxonomic

variability and nutrient utilization and primary production in the Ross

Sea. Journal of Geophysical Research 105, 8827–8846.

Buma, A.G.J., de Boer, M.K., Boelen, P., 2001. Depth distributions of

DNA damage in Antarctic marine phyto- and bacterioplankton

exposed to summertime ultraviolet radiation. Journal of Phycology

37, 200–208.

Delille, B., 2006. Inorganic carbon dynamics and air–ice–sea CO2 fluxes in

the open and coastal waters of the Southern Ocean. Ph.D. Thesis,

Universite de Liege, 297pp.

DiTullio, G.R., Garrison, D.L., Mathot, S., 1998. Dimethylsulfoniopro-

pionate in sea ice algae from the Ross Sea polynya. In: Lizotte, M.P.,

Arrigo, K.R. (Eds.), Antarctic Sea Ice Biological Processes, Interac-

tions and Variability. American Geophysical Union, Washington, DC,

pp. 139–146.

Eisen, O., Kottmeier, C., 2000. On the importance of leads in sea ice to the

energy balance and ice formation in the Weddell Sea. Journal of

Geophysical Research 105, 14,045–14,060.

Gibson, J.A.E., Trull, T., Nichols, P.D., Summons, R.E., McMinn, A.,

1999. Sedimentation of 13C-rich organic matter from Antarctic sea-ice

algae: a potential indicator of past sea ice extent. Geology 27, 331–334.

Gleitz, M., Grossmann, S., Scharek, R., Smetacek, V., 1996. Ecology of

diatom and bacterial assemblages in water associate with melting

summer sea ice in the Weddell Sea, Antarctica. Antarctic Science 8,

135–146.

Gloersen, P., Campbell, W.J., Cavalieri, D.J., Comiso, J.C., Parkinson,

C.L., Zwally, H.J., 1992. Arctic and Antarctic Sea Ice, 1978–1987:

Satellite Passive-Microwave Observations and Analysis. NASA SP-

511, Washington, DC, 290pp.

Golden, K.M., Ackley, S.F., Lytle, V.I., 1998. The percolation phase

transition in sea ice. Science 282, 2238–2241.

Grasshoff, K., Ehrhardt, M., Kremling, K., 1983. Methods of Seawater

Analysis. Verlag Chemie, Weinheim, Germany.

Haas, L.W., 1982. Improved epifluorescence microscopy for observing

planktonic micro-organisms. Annales de l’Institut Oceanographique

58, 261–266.

Hales, B., van Greer, A., Takahashi, T., 2004. High-frequency measure-

ments of seawater chemistry: flow-injection analysis of macronutrients.

Limnology and Oceanography: Methods 2, 91–101.

Hatton, A.D., 2002. Influence of photochemistry on the marine

biogeochemical cycle of dimethylsulphide in the northern North Sea.

Deep-Sea Research II 49, 3039–3052.

Hatton, A.D., Darroch, L., Malin, G., 2004. The role of dimethylsulph-

oxide in the marine biogeochemical cycle of dimethylsulphide.

Oceanography and Marine Biology—An Annual Review 42, 29–55.

Helcom, 1988. Guidelines for the Baltic Monitoring programme third

stage: Part D. Biological determinants. In: Baltic Sea Environmental

Proceedings, 27D, Helsinki Commission.

Holmes, R.M., Aminot, A., Kerouel, R., Hocker, B.A., Peterson, B.J.,

1999. A simple and precise method for measuring ammonium in

marine and fresh water. Canadian Journal of Fisheries and Aquatic

Sciences 56, 1801–1808.

Kattner, G., Becker, H., 1991. Nutrients and organic nitrogenous

compounds in the marginal ice zone of the Farm Strait. Journal of

Marine Systems 2, 385–394.

Kattner, G., Thomas, D.N., Haas, C., Kennedy, H., Dieckmann, G.S.,

2004. Surface ice gab layers in Antarctic sea ice: highly productive

habitats. Marine Ecology—Progress Series 277, 1–12.

Kieber, D.J., Jianfu, J., Kiene, R.P., Bates, T.S., 1996. Impact of

dimethylsulfide photochemistry on methyl sulfur cycling in the

equatorial Pacific Ocean. Journal of Geophysical Research 101,

3715–3722.

ARTICLE IN PRESSH.J. Zemmelink et al. / Deep-Sea Research II 55 (2008) 988–999 999

Kroon, H., 1993. Determination of nitrogen in water: comparison of

continuous flow method with on-line UV digestion with the original

Kjedahl method. Analytica Chimica Acta 276, 287–293.

Lancelot, C., Veth, C., Mathot, S., 1991. Modelling ice edge phytoplank-

ton bloom in the Scotia Weddell Sea sector of the Southern Ocean

during spring 1988. Journal of Marine Systems 2, 333–346.

Lancelot, C., Mathot, S., Veth, C., de Baar, H., 1993. Factors controlling

phytoplankton ice-edge blooms in the marginal ice-zone of the north-

western Weddell Sea during sea ice retreat 1988: field observations and

mathematical modeling. Polar Biology 13, 377–387.

Lizotte, M.P., 2003. The microbiology of sea ice. In: Thomas, D.N.,

Dieckmann, G.S. (Eds.), Sea Ice—An Introduction to its Physics,

Chemistry, Biology and Geology. Blackwell, Oxford, pp. 184–210.

Mitchell, B.G., Holm-Hansen, O., 1991. Bio-optical properties of

Antarctic Peninsula waters: differentiation from temperate ocean

models. Deep-Sea Research 38, 1009–1028.

Palmisano, A.C., SooHoo, J.B., SooHoo, S.L., Kottmeier, S.T., Craft,

L.L., Sullivan, C.W., 1986. Photo-adaption in Phaeocystis pouchetii

advected beneath annual ice in McMurdo Sound, Antarctica. Journal

of Plankton Research 8 (6), 891–906.

Richardson, K., Beardall, J., Raven, A., 1983. Adaptation of unicellular

algae to irradiance: an analysis of strategies. New Phytologist 93,

157–191.

Schloss, I., Estrada, M., 1994. Phytoplankton composition in the Weddell-

Scotia Confluence area during austral spring in relation to hydro-

graphy. Polar Biology 14, 77–90.

Schroder, M., Wisotzki, A., Brunken, N., Hansen, I., Heil, P., Kreyscher,

M., Moschner, S., Steiner, N., Sterr, U., Richter, K., Diedrich, H.,

1994. Physical oceanography and nutrients. In: Lemke, P. (Ed.), The

Expedition ANTARKTIS X/4 of RV ‘‘Polarstern’’ in 1992. Berichte

zur Polarforschung, vol. 140, pp. 15–34.

Semiletov, I., Makshtas, A., Akasofu, S.I., Andreas, E.L., 2004. Atmo-

spheric CO2 balance: the role of Arctic sea ice. Geophysical Research

Letters 31, L05121.

Smith Jr., W.O., Nelson, D.M., 1986. Importance of ice-edge

phytoplankton production in the Southern Ocean. BioScience 36,

251–256.

Smith Jr., W.O., Gordon, L.I., 1997. Hyperproductivity of the Ross Sea

(Antarctica) polynya during austral spring. Geophysical Research

Letters 24, 233–236 (stratified euphotic zone of the North Sea. Deep-

Sea Research 49, 3017–3038).

Sunda, W., Kieber, D.J., Kiene, R.P., Huntsman, S., 2002. An antioxidant

function for DMSP and DMS in marine algae. Nature 418, 317–320.

Sweeney, C., Smith, W.O., Hales, B., Bidigare, R.R., Carlson, C.A.,

Codispoti, L.A., Gordon, L.I., Hansell, D.A., Millero, F.J., Park, M.,

Takahashi, T., 2000. Nutrient and carbon removal ratios and fluxes in

the Ross Sea, Antarctica. Deep-Sea Research II 47, 3395–3421.

Thomas, D.N., Dieckmann, G.S., 2002. Antarctic sea ice—a habitat for

extremophiles. Science 295, 641–644.

Thomas, D.N., Dieckmann, G.S. (Eds.), 2003. Sea Ice—An Introduction

to its Physics, Chemistry, Biology and Geology. Blackwell, Oxford,

416pp.

Thomas, D.N., Kennedy, H., Kattner, G., Gerdes, D., Gough, C.,

Dieckmann, G.S., 2001. Biogeochemistry of platelet ice: its influence

on particle flux under fast ice in the Weddell Sea, Antarctica. Polar

Biology 24, 486–496.

Tilzer, M.M., Elbrachter, M., Gieskes, W.W.C., Beese, B., 1986. Light–

temperature interactions in the control of photosynthesis in Antarctic

phytoplankton. Polar Biology 5, 105–111.

Trevena, A.J., Jones, G.B., 2006. Dimethylsulphide and dimethylsulpho-

niopropionate in Antarctic sea ice and their release during sea ice

melting. Marine Chemistry 98, 210–222.

Trevena, A.J., Jones, G.B., Wright, S.W., van den Enden, R.L., 2003.

Profiles of dimethylsulphoniopropionate (DMSP), algal pigments,

nutrients, and salinity in the fast ice of Prydz Bay, Antarctica. Journal

of Geophysical Research 108.

van de Poll, W.H., van Leeuwe, M.A., Roggeveld, J., Buma, A.G.J., 2005.

Nutrient limitation and high irradiance acclimation reduce PAR and

UV-induced viability in the Antarctic diatom Chaetoceros brevis

(Bacillariophyceae). Journal of Phycology 41, 840–850.

Wedborg, M., Hoppema, M., Skoog, A., 1998. On the relation between

organic and inorganic carbon in the Weddell Sea. Journal of Marine

Systems 17, 59–76.

Winston, G.W., 1990. Physicochemical basis for free radical formation in

cells: production and defense. In: Alscher, R.G., Cumming, J.R.

(Eds.), Stress Response in Plants: Adaptation and Acclimation

Mechanisms. Wiley, New York, pp. 58–86.

Zemmelink, H.J., Houghton, L., Dacey, J.W.H., Worby, A., Liss, P.S.,

2005a. Emission of dimethylsulfide from Weddell Sea leads. Geophy-

sical Research Letters 32, L23610.

Zemmelink, H.J., Houghton, L., Frew, N.M., Dacey, J.W.H., 2005b.

Gradients in dimethylsulfide, dimethylsulfoniopropionate, dimethyl-

sulfoxide, and bacteria near the sea surface. Marine Ecology—

Progress Series 295, 33–42.

Zemmelink, H.J., Delille, B., Hintsa, E.J., Houghton, L., Dacey, J.W.H.,

2006a. CO2 deposition over the multi year ice of the western Weddell

Sea. Geophysical Research Letters 33, L13606.

Zemmelink, H.J., Houghton, L., Frew, N.M., Dacey, J.W.H., 2006b.

Dimethylsulfide and major sulfur compounds in a stratified coastal salt

pond. Limnology and Oceanography 51, 271–279.