Antarctic Phytoplankton Research Articles

Limitation by Fe, Zn, Co, and B12 Results in Similar Physiological Responses in Two Antarctic Phytoplankton Species

In many areas of the world’s ocean such as the Southern Ocean (SO), primary production is low despite an abundance of macronutrients. In these high nutrient low chlorophyll (HNLC) regions the trace metal (TM) iron (Fe) limits phytoplankton biomass and subsequently the biological carbon pump. Besides Fe, the TMs zinc (Zn), cobalt (Co) and the vitamin cobalamin (B12) have also been shown to limit biomass and/or influence plankton species composition. While the impacts of Fe limitation and, to a lesser degree of Zn and Co, on the cellular physiology of Antarctic phytoplankton have been investigated, studies focusing simultaneously on several TMs and vitamins are still lacking. This study measured the impacts of Fe, Zn, Co and B12 limitation on the Antarctic diatom Chaetoceros simplex and Fe and Zn limitation on the Antarctic cryptophyte Geminigera cryophila. Both species responded to all limitation scenarios by reducing their growth and particulate organic carbon production rates. For both algae limitation by Fe and Zn resulted in a reduction of light harvesting pigments, a significant reduction in the photosynthetic yield (Fv/Fm) and increase in the C:N ratio. Most interestingly, with a few exceptions, limitation by one TM also resulted in a significant decrease of the cellular quotas of other TMs measured. These observations suggest that one consequence of limitation by one TM may be a secondary and perhaps more fatal limitation by another.

Combined effects of temperature and salinity on fatty acid content and lipid damage in Antarctic phytoplankton

We investigated the effects of ocean warming and glacial melting on phytoplankton assemblage composition and physiology in coastal Antarctica by exposing assemblages to a 4 °C increase in seawater temperature (T) and a 4 psu decrease in salinity (S) with respect to ambient values in a 6-day microcosm experiment. Seawater samples from Potter Cove in King George Island (Antarctica) were placed in outdoor microcosms and exposed to four treatments: ambient S-ambient T (S0T0, control), low S-ambient T (S-T0), ambient S-high T (S0T+), and low S-high T (S-T+). The relative abundance of unsaturated fatty acids (UFAs) 20:5ω3, 18:4ω3 and 16:1ω7 in relation to saturated FAs (14:0 and 16:0) significantly increased in all treatments at 24 h, compared to the control. At the same time, we detected a significant increase in the production of Thiobarbituric Acid Reactive Substances (TBARS), used as a proxy for lipid damage, in the S-T0 and the S0T+ treatments. In contrast, in S-T+, concentrations of TBARS remained significantly lower than in the control throughout the experiment. Although phytoplankton species composition did not change during the experiment, an increase in the relative abundance of diatoms (>20 μm) was found in all treatments compared to the control at 24 h, with no further changes during the rest of the experiment. Furthermore, the relative abundance of small diatoms (10–20 μm) increased only in S0T+, and small prasinophytes decreased at S-T+ at the end of the incubation period.Our results show a stable unsaturated to saturated FA ratio under the synergistic effects of high temperature and lower salinity, which may help protect phytoplankton cells from lipid damage. When phytoplankton assemblages were exposed to high temperature or low salinity, separately, the proportion of unsaturated FAs increased after 48 h. This increase in FAs resulted in greater lipid damage, which could be potentially avoided, as shown by previous studies, by antioxidant responses or changes in osmoregulatory proteins and FA synthesis by the activation or inactivation of desaturase enzymes. Variations in FA content due to changing environmental conditions can alter the quality of phytoplankton as a food source with potentially critical implications for the marine food web.

Interactions of dissolved CO2 with cadmium isotopes in the Southern Ocean

Abstract Here we report the first ever observations of a strong correlation in ocean surface waters of the dissolved δ 114 Cd with dissolved CO 2 . This is observed in the Southern Ocean along the 0°W meridian in both the Antarctic Circumpolar Current and the Weddell Gyre, as well as in the Weddell Sea proper, near the Antarctic Peninsula and in Drake Passage. This uniform trend in several surface water masses hints at a uniform biochemical mechanism within the Southern Ocean. One hypothesis for the underlying mechanism would be a role of Cd in the carbonic anhydrase function for conversion of bicarbonate ion [HCO 3 − ] into CO 2 , the latter being required by RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) that only accepts CO 2 . At low ambient [CO 2 ] the algae maintain growth by also operating a Carbon Concentrating Mechanism (CCM) for utilization of [HCO 3 − ] and its conversion to CO 2 . For this the algae need more enzyme carbonic anhydrase that normally has Zn as its co-factor, but Cd may substitute for Zn and there also are Cd-specific carbonic anhydrases known for some phytoplankton species. Indeed in incubations of the local plankton communities it is shown that the phytoplankton have a very strong preferential uptake of CO 2 , such that the uptake ratio {[CO 2 ]/[HCO 3 − ]} is much higher than the dissolved ratio {[CO 2 ]/[HCO 3 − ]} in ambient seawater. Therefore the here reported observations in the Southern Ocean are also expressed for δ 114 Cd as function of the ratio {[CO 2 ]/[HCO 3 − ]} in ambient seawater. Future research of local phytoplankton in unperturbed natural waters of the Southern Ocean is recommended to be able to verify the hypothesis of a function of Cd in carbonic anhydrase in Antarctic phytoplankton.

John A. Raven.

John A. Raven.

Annual boom–bust cycles of polar phytoplankton biomass revealed by space-based lidar

Polar plankton communities are among the most productive, seasonally dynamic and rapidly changing ecosystems in the global ocean. However, persistent cloud cover, periods of constant night and prevailing low solar elevations in polar regions severely limit traditional passive satellite ocean colour measurements and leave vast areas unobserved for many consecutive months each year. Consequently, our understanding of the annual cycles of polar plankton and their interannual variations is incomplete. Here we use space-borne lidar observations to overcome the limitations of historical passive sensors and report a decade of uninterrupted polar phytoplankton biomass cycles. We find that polar phytoplankton dynamics are categorized by ‘boom–bust’ cycles resulting from slight imbalances in plankton predator–prey equilibria. The observed seasonal-to-interannual variations in biomass are predicted by mathematically modelled rates of change in phytoplankton division. Furthermore, we find that changes in ice cover dominated variability in Antarctic phytoplankton stocks over the past decade, whereas ecological processes were the predominant drivers of change in the Arctic. We conclude that subtle and environmentally driven imbalances in polar food webs underlie annual phytoplankton boom–bust cycles, which vary interannually at each pole. Phytoplankton productivity is high in the polar oceans. Lidar observations from 2006–2015 reveal that phytoplankton biomass was characterized by annual cycles influenced by sea-ice extent in the Antarctic and ecological processes in the Arctic.

The genus Chaetoceros (Bacillariophyta) in Arctic and Atarctic

A floristic review of the genus Chaetoceros from Arctic and Antarctic waters is undertaken. Taxonomic composition of the Chaetoceros from the Russian Arctic seas, as well as from some regions of the Antarctic was investigated in both water column and sea ice. The genus is rather diverse in both polar regions: 55 species in Arctic and 34 ones in Antarctic. The regions differ in total number of species, number of species belonging to the subgenera Chaetoceros and Hyalochaete and to different sections. Species of the genus are often dominant and the most abundant in Arctic phytoplankton. However, the genus is not prevailing in number of the dominant species as well as in share of the total cell abundance of Antarctic phytoplankton. The importance of the species in sea ice assemblages of the Antarctic is more significant as compared with the Arctic. The Arctic is characterized by cosmopolitan species and those widely distributed in the Northern Hemisphere, more than half of the Chaetoceros taxa are common to all Arctic seas. The Antarctic has a high percentage of endemic Chaetoceros species. Both polar regions are similar in terms of Chaetoceros species composition mainly due to cosmopolitan species.

Antarctic phytoplankton down-regulate their carbon-concentrating mechanisms under high CO2 with no change in growth rates

Antarctic phytoplankton down-regulate their carbon-concentrating mechanisms under high CO2 with no change in growth rates

Effects of salinity changes on coastal Antarctic phytoplankton physiology and assemblage composition

A natural marine phytoplankton assemblage from a coastal environment of Antarctica was experimentally exposed to low salinity sea water (30 vs 34 in the control) during 8days in order to study their physiological and community responses to hypoosmotic stress conditions. Hypoosmotic conditions favour water influx into the cells, which results in increased turgor pressure and increased oxidative stress. This stress is linked to a number of other cellular toxic processes, including damages to proteins, enzyme inactivation and DNA breakage. Inhibition of the instantaneous growth rate started after 48h exposure to low salinity, but at the end of experiment, growth was significantly higher in the low than in the normal (control) salinity treatment. Hypoosmotic conditions prevented phytoplankton biomass accumulation, as evidenced by reduced Chlorophyll-a concentrations as compared to the control treatment. However, in terms of cell numbers and species composition, we observed a gradual replacement of big centric by small pennate diatoms, which became dominant by the end of the experiment. In addition, the content of reactive oxygen species (ROS) and 2-thiobarbituric acid-reactive substances (TBARS), which are indicative of oxidative stress, were studied. In the low salinity treatments, ROS concentrations were significantly higher than control values on days 4 and 6, decreasing thereafter to nearly initial values. TBARS content increased during the first 48h and then decreased until around day 0 values. This coincided with significant increased values of the antioxidants α-tocopherol and β-carotene in low salinity treatments over the control. These results suggest the existence of protection mechanisms against lipid peroxidation, and lead to the conclusion that the response to stress is species-specific, so that at the community level a change in the relative abundance of phytoplankton taxa appears as a response to hypoosmotic conditions. This could have important consequences for the trophic food web dynamics in areas influenced by high fresh water inputs.

Comparative responses of two dominant Antarctic phytoplankton taxa to interactions between ocean acidification, warming, irradiance, and iron availability

We investigated the responses of the ecologically dominant Antarctic phytoplankton species Phaeocystis antarctica (a prymnesiophyte) and Fragilariopsis cylindrus (a diatom) to a clustered matrix of three global change variables (CO2, mixed‐layer depth, and temperature) under both iron (Fe)‐replete and Fe‐limited conditions based roughly on the Intergovernmental Panel on Climate Change (IPCC) A2 scenario: (1) Current conditions, 39 Pa (380 ppmv) CO2, 50 µmol photons m−2 s−1 light, and 2°C; (2) Year 2060, 61 Pa (600 ppmv) CO2, 100 µmol photons m−2 s−1 light, and 4°C; (3) Year 2100, 81 Pa (800 ppmv) CO2, 150 µmol photons m−2 s−1 light, and 6°C. The combined interactive effects of these global change variables and changing Fe availability on growth, primary production, and cell morphology are species specific. A competition experiment suggested that future conditions could lead to a shift away from P. antarctica and toward diatoms such as F. cylindrus. Along with decreases in diatom cell size and shifts from prymnesiophyte colonies to single cells under the future scenario, this could potentially lead to decreased carbon export to the deep ocean. Fe : C uptake ratios of both species increased under future conditions, suggesting phytoplankton of the Southern Ocean will increase their Fe requirements relative to carbon fixation. The interactive effects of Fe, light, CO2, and temperature on Antarctic phytoplankton need to be considered when predicting the future responses of biology and biogeochemistry in this region.

Species-Specific Variations in the Nutritional Quality of Southern Ocean Phytoplankton in Response to Elevated pCO2

Increased seawater pCO2 has the potential to alter phytoplankton biochemistry, which in turn may negatively affect the nutritional quality of phytoplankton as food for grazers. Our aim was to identify how Antarctic phytoplankton, Pyramimonas gelidicola, Phaeocystis antarctica, and Gymnodinium sp., respond to increased pCO2. Cultures were maintained in a continuous culture setup to ensure stable CO2 concentrations. Cells were subjected to a range of pCO2 from ambient to 993 µatm. We measured phytoplankton response in terms of cell size, cellular carbohydrate content, and elemental, pigment and fatty acid composition and content. We observed few changes in phytoplankton biochemistry with increasing CO2 concentration which were species-specific and predominantly included differences in the fatty acid composition. The C:N ratio was unaffected by CO2 concentration in the three species, while carbohydrate content decreased in Pyramimonas gelidicola, but increased in Phaeocystis antarctica. We found a significant reduction in the content of nutritionally important polyunsaturated fatty acids in Pyramimonas gelidicola cultures under high CO2 treatment, while cellular levels of the polyunsaturated fatty acid 20:5ω3, EPA, in Gymnodinium sp. increased. These changes in fatty acid profile could affect the nutritional quality of phytoplankton as food for grazers, however, further research is needed to identify the mechanisms for the observed species-specific changes and to improve our ability to extrapolate laboratory-based experiments on individual species to natural communities.

Short- and long-term response of phytoplankton to ENSO in Prydz Bay, Antarctica: Evidences from field measurements, remote sensing data and stratigraphic biomarker records

The study provides one of the first lines of evidence showing linkages between Antarctic phytoplankton abundance and composition in response to ENSO, based on historical reconstruction of sediment biomarkers. In addition to sediment biomarkers, field measured and remote sensing data of phytoplankton abundance were also recorded from Prydz Bay, Eastern Antarctica. Community structure of field measured phytoplankton showed significant El Nino/La Nina-related succession during 1990 to 2002. In general, the number of algae species decreased during El Nino and La Nina years compared to normal years. Austral summer monthly variation of remotely sensed chlorophyll-a (Chl-a), particulate organic carbon (POC), and sea surface temperature (SST) indicated that ENSO impacted the timing of phytoplankton blooms during 2007 to 2011. Phytoplankton blooms (indicated by Chl-a and POC) preceded the increases in SST during El Nino years, and lagged behind the SST increases during La Nina years. Stratigraphic record of marine sedimentary lipid (brassicasterol, dinosterol and alkenones) biomarkers inferred that the proportions of different algae (diatoms, dinoflagellates and haptophytes) changed significantly between El Nino and La Nina events. The relative proportion of diatoms increased, with that of dinoflagellates being decreased during El Nino years, while it was reversed during La Nina years.

Rapid DMSP production by an Antarctic phytoplankton community exposed to natural surface irradiances in late spring

Natural marine microbial communities sourced from under fast ice at an Antarctic coastal site were incubated in tanks under differently attenuated natural sunlight for 2 wk in late spring (Expt 1) and early summer (Expt 2). In the 18 d period between the 2 sampling episodes, the ice edge retreated from 10 to within 1.5 km of the sampling site, and the fast ice began to break up. Expt 1 rapidly produced significant quantities of total DMSP (DMSPt) with concentrations increasing from 16.6 nmol l �1 to 192.7�204.5 nmol l �1 in 2 d. We believe this is the largest observed increase in DMSPt in a semi-natural community over this time frame. Abundances of Phaeocystis antarctica increased significantly during this initial period, while other phytoplankton species/ groups remained stable. DMSPt concentrations then declined at rates averaging 39.2� 50.0 nmol l �1 d �1 between Days 2 and 4. No major DMSPt production event occurred during Expt 2 despite strong community similarities. Sea ice breakout exposes phytoplankton to significant light-related oxidative stress, and these results suggest the rapid production of DMSPt during Expt 1 was due to the initiation of anti-oxidant mechanisms by a low-light-acclimated community in response to solar radiation stress. DMS concentrations remained comparatively low throughout Expt 1, sug- gesting oxidation of DMSP to products other than DMS. Rapid sea ice breakout in coastal regions of Antarctica may result in similar fast DMSP production events during spring.

Tolerance of polar phytoplankton communities to metals

Large amounts of pollutants reach polar regions, particularly the Arctic, impacting their communities. In this study we analyzed the toxic levels of Hg, Cd and Pb to natural phytoplankton communities of the Arctic and Southern Oceans, and compared their sensitivities with those observed on phytoplankton natural communities from temperate areas. Mercury was the most toxic metal for both Arctic and Antarctic communities, while both Cd and Pb were toxic only for the Antarctic phytoplankton. Total cell abundance of the populations forming the Arctic community increased under high Cd and Pb concentrations, probably due to a decrease of the grazing pressure or the increase of the most resistant species, although analysis of individual cells indicated that cell death was already induced at the highest levels. These results suggest that phytoplankton may have acquired adapting mechanisms to face high levels of Pb and Cd in the Arctic Ocean.

Sensitivity of Antarctic phytoplankton species to ocean acidification: Growth, carbon acquisition, and species interaction

Despite the fact that ocean acidification is considered to be especially pronounced in the Southern Ocean, little is known about CO2‐dependent physiological processes and the interactions of Antarctic phytoplankton key species. We therefore studied the effects of CO2 partial pressure (PCO2) (16.2, 39.5, and 101.3 Pa) on growth and photosynthetic carbon acquisition in the bloom‐forming species Chaetoceros debilis, Pseudo‐nitzschia subcurvata, Fragilariopsis kerguelensis, and Phaeocystis antarctica. Using membrane‐inlet mass spectrometry, photosynthetic O2 evolution and inorganic carbon (Ci) fluxes were determined as a function of CO2 concentration. Only the growth of C. debilis was enhanced under high PCO2. Analysis of the carbon concentrating mechanism (CCM) revealed the operation of very efficient CCMs (i.e., high Ci affinities) in all species, but there were species‐specific differences in CO2‐dependent regulation of individual CCM components (i.e., CO2 and uptake kinetics, carbonic anhydrase activities). Gross CO2 uptake rates appear to increase with the cell surface area to volume ratios. Species competition experiments with C. debilis and P. subcurvata under different PCO2 levels confirmed the CO2‐stimulated growth of C. debilis observed in monospecific incubations, also in the presence of P. subcurvata. Independent of PCO2, high initial cell abundances of P. subcurvata led to reduced growth rates of C. debilis. For a better understanding of future changes in phytoplankton communities, CO2‐sensitive physiological processes need to be identified, but also species interactions must be taken into account because their interplay determines the success of a species.

Dark survival in a warming world

Most algae regularly experience periods of darkness ranging from a few hours to a few days. During this time, they are unable to photosynthesize, and so must consume stored energy products. However, some organisms such as polar algae and some microalgal cysts and spores are exposed to darkness for months to years, and these must use alternative strategies to survive. Some taxa, such as dinoflagellates, form cysts and become dormant. Others use physiological methods or adopt mixotrophy. The longest documented survival of more than a century was for dinoflagellates buried in sediments in a Norwegian fjord. Seasonal changes in daylight hours are naturally unaffected by climate change. This means that polar microalgae will in the future need to survive the same period of seasonal darkness but at higher temperatures, and this will require a greater drawdown of stored energy. Recent experimental work has shown that both Arctic and Antarctic phytoplankton are able to survive increases of up to 6°C in the dark.

Shifts in the dominance between diatoms and cryptophytes during three late summers in the Bransfield Strait (Antarctic Peninsula)

Recent global warming reduces surface water salinity around the Antarctic Peninsula as a result of the glacial meltwater runoff, which increases the occurrence and abundance of certain phytoplankton groups, such as cryptophytes. The dominance of this particular group over diatoms affects grazers, such as Antarctic krill, which preferentially feed on diatoms. Using three late summer data sets from the Bransfield Strait (2008–2010), we observed variations in the dominant phytoplankton groups determined by HPLC/CHEMTAX pigment analysis and confirmed by microscopy. Results indicate that the dominance of diatoms, particularly in 2008 and 2009, was associated with a deeper upper mixed layer (UML), higher salinity and warmer sea surface temperature. In contrast, cryptophytes, which were dominant in 2010, were associated with a shallower UML, lower salinity and colder sea surface temperatures. The low diatom biomass observed in the summer of 2010 was associated with high nutrient concentration, particularly silicate, and low chlorophyll a (summer monthly average calculated from satellite images). The interannual variability here observed suggests a delayed seasonal succession cycle of phytoplankton in the summer of 2010 associated with a cold summer and a late ice retreat process in the region. This successional delay resulted in a notable decrease of primary producers’ biomass, which is likely to have impacted regional food web interactions. This study demonstrates the susceptibility of the Antarctic phytoplankton community structure to air temperature, which directly influences the timing of ice melting and consequently the magnitude of primary production and succession pattern of phytoplankton groups.

Spatial variation of phytoplankton assemblages and biomass in the New Zealand sector of the Southern Ocean during the late austral summer 2008

Up until now, only the floristic composition of large phytoplankton species has been studied in the Southern Ocean immediately south of New Zealand. To fill the gaps in our knowledge of the Antarctic phytoplankton flora and biomass, in relation to physical and chemical environments, New Zealand’s IPY project sampled water between New Zealand and Antarctica and into the Ross Sea in late summer. Near surface phytoplankton samples, collected between New Zealand and Antarctica, and vertical stations, between Scott Island and the Ross Sea ice shelf, allowed us to contrast the flora and biomass in the Ross Sea/Antarctic and Subantarctic waters. Spatially, diatoms were found to be more diverse in both shelf and offshore Antarctic than in Subantarctic waters. Over the Ross Sea shelf, the pennate diatom, Fragilariopsis kerguelensis, and a colonial prymnesiophyte, Phaeocystis antarctica, dominated both numerically and in biomass, contributing to greatest levels of chlorophyll a and cell carbon biomass over the shelf. In both shelf and Antarctic waters, heterotrophic taxa accounted for a greater proportion of total dinoflagellate cell carbon (avg. 95.4 and 91.9 %, respectively) than autotrophic, while in the Subantarctic waters, the reverse was true (avg. 48.6 %). A small number of potentially harmful dinoflagellates, Karenia and Karlodinium spp., were found for the first time in the New Zealand sector of the Southern Ocean. This study represents the first thorough description of the spatial variation of the floristic composition and biomass of phytoplankton in relation to physical and chemical properties, from New Zealand to Antarctica.

The physiological response to increased temperature in over-wintering sea ice algae and phytoplankton in McMurdo Sound, Antarctica and Tromsø Sound, Norway

The physiological response to increased temperature during dark exposure was examined in phytoplankton and sea ice algae that had overwintered in McMurdo Sound, Antarctica and Tromsø Sound, Norway. Under ice phytoplankton and sea ice algae from McMurdo Sound were incubated in the dark for 22days and 23days respectively at −2, 4 and 10°C, while phytoplankton from Tromsø Sound were incubated for 35days at 4, 10 and 20°C. A fluorescence approach was used to examine algal photophysiology (Fv/Fm, rETRmax and α) and changes in the concentration of chlorophyll a, while the spectrophotometric 2,4,6-tripyridyl-s-triazine (TPTZ) assay was used to quantify water-extractable carbohydrates. Prior to incubation, the photosynthetic parameters documented relatively healthy overwintering communities for both polar regions. Elevated temperature had a considerable impact on the dark survival of Arctic phytoplankton, and, to a lesser extent, Antarctic sea ice algae: photosynthetic health and stored monosaccharides declined during the incubation period, particularly at the warmest temperature regimes. In contrast, the concentration of chlorophyll a and polysaccharides remained relatively constant. When Antarctic sea ice algae were subsequently exposed to low light (~20μmol photons m−2s−1), significant photosynthetic recovery was only observed in cultures maintained at −2°C. A more robust response to increased temperature was observed in Antarctic phytoplankton and in general, variability between the −2°C and 4°C (Antarctic) and 4°C and 10°C (Arctic) temperature regimes was minimal, which suggests that increasing temperature will not limit the ability of phytoplankton to survive the polar winter and provide the inocula for bloom events.

Primary production throughout austral fall, during a time of decreasing daylength in the western Antarctic Peninsula

Antarctic phytoplankton is characterized by a pronounced seasonality in abundance, driven mainly by changes in sunlight. We combined measurements and modeling to describe the influence of changing daylength on fall and winter phytoplankton production in coastal waters of the western Antarctic Peninsula (wAP) in 2001 and 2002. The model was parameterized with field observations from the Palmer Long-Term Ecological program in the wAP during summer and early fall and from the Southern Ocean Global Ecosystems Dynamics program fall and winter cruises to Marguerite Bay and shelf waters. Shorter daylength and a deepening of the mixed layer account for most of the decrease in primary production during March, April, and May. At this time, biomass decreases by an order of magnitude and remains low and constant until the end of August. An additional loss rate was added to the primary production model to fit output to obser- vations. This loss rate, estimated at ~0.1 to 0.15 d �1 , is due to physical, chemical, and biological processes such as scavenging by sea ice, zooplankton grazing, cell lysis, and cell sedimentation, which are expected to be high at this time of year. Growth and loss rates of phytoplankton popu- lations are similar on 1 March, with growth decreasing rapidly over time while the loss rates remain constant. By the beginning of winter (1 June), growth is low, with minimum rates in July and increasing towards September. During a period of diminishing food supply, preliminary esti- mates of grazing indicate that fall biomass could support existing macrozooplankton populations, but the timing and concentration of food supply is variable and expected to affect health of zoo- plankton as they enter the winter.

Highly branched isoprenoids as proxies for variable sea ice conditions in the Southern Ocean

AbstractConcentrations of a highly branched isoprenoid (HBI) diene determined in over 200 sediment samples from the Arctic co-vary with those of an HBI monoene (IP25) shown previously to be a sedimentary sea ice proxy for the Arctic. The same diene, but not monoene IP25, occurred in nine sea ice samples collected from various locations around Antarctica. The diene has been reported previously in Antarctic sea ice diatoms and the 13C isotopic compositions of the diene determined in two Antarctic sea ice samples were also consistent with an origin from sea ice diatoms (δ13C -5.7 to -8.5‰). In contrast, HBIs found in two Antarctic phytoplankton samples did not include the diene but comprised a number of tri- to pentaenes. In sediment samples collected near Adélie Land, East Antarctica, both the diene and the tri- to pentaenes often co-occurred. 13C isotopic compositions of the tri- to pentaenes in three sediment samples ranged from -35 to -42‰ whereas that of the diene in a sediment sample was -18‰. We propose the presence of this isotopically 13C enriched HBI diene in Antarctic sediments to be a useful proxy indicator for contributions of organic matter derived from sea ice diatoms. A ratio of the concentrations of diene/trienes might reflect the relative contributions of sea ice to phytoplanktonic inputs of organic matter to Antarctic sediments.