David N. Thomas

Large scale importance of sea ice biology in the Southern Ocean

Despite being one of the largest biomes on earth, sea ice ecosystems have only received intensive study over the past 30 years. Sea ice is a unique habitat for assemblages of bacteria, algae, protists, and invertebrates that grow within a matrix dominated by strong gradients in temperature, salinity, nutrients, and UV and visible radiation. A suite of physiological adaptations allow these organisms to thrive in ice, where their enormous biomass makes them a fundamental component of polar ecosystems. Sea ice algae are an important energy and nutritional source for invertebrates such as juvenile krill, accounting for up to 25% of total annual primary production in ice-covered waters. The ability of ice algae to produce large amounts of UV absorbing compounds such as mycosporine-like amino acids makes them even more important to organisms like krill that can incorporate these sunscreens into their own tissues. Furthermore, the nutrient and light conditions in which sea ice algae thrive induce them to synthesize enhanced concentrations of polyunsaturated fatty acids, a vital constituent of the diet of grazing organisms, especially during winter. Finally, sea ice bacteria and algae have become the focus of biotechnology, and are being considered as proxies of possible life forms on ice-covered extraterrestrial systems. An analysis of how the balance between sea ice and pelagic production might change under a warming scenario indicates that when current levels of primary production and changes in the areas of sea ice habitats are taken into account, the expected 25% loss of sea ice over the next century would increase primary production in the Southern Ocean by approximately 10%, resulting in a slight negative feedback on climate warming.

Comparison of summer and winter inorganic carbon, oxygen and nutrient concentrations in Antarctic sea ice brine

Abstract During summer (January 1991) and winter (April 1992) cruises to the southern Weddell Sea (Antarctica), brine samples were collected from first year sea ice and analysed for salinity, temperature, dissolved oxygen and major nutrient concentrations. Additionally, the carbonate system was determined from measurements of pH and total alkalinity. During winter, brine chemical composition was largely determined by seawater concentration in the course of freezing. Brine temperatures ranged from −1.9 to −6.7 °C. Precipitation of calcium carbonate was not observed at the corresponding salinity range of 34 to 108. Removal of carbon from the total inorganic carbon pool (up to 500 μmol C t kg −1 ) was related to reduced nutrient concentrations, indicating the presence of photosynthetically active ice algal assemblages in the winter sea ice. However, nutrient and inorganic carbon concentrations did generally not reach growth limiting levels for phytoplankton. The combined effect of photosynthesis and physical concentration resulted in O 2 concentrations of up to 650 μmol kg −1 . During summer, brine salinities ranged from 21 to 41 with most values > 28, showing that the net effect of freezing and melting on brine chemical composition was generally slight. Opposite to the winter situation, brine chemical composition was strongly influenced by biological activity. Photosynthetic carbon assimilation resulted in a C t depletion of up to 1200 μmol kg −1 , which was associated with CO 2 (aq) exhaustion and O 2 concentrations as high as 933 μmol kg −1 . The concurrent depletion of major nutrients generally corresponded to uptake ratios predicted from phytoplankton biochemical composition. Primary productivity in summer sea ice is apparently sustained until inorganic resources are fully exhausted, resulting in brine chemical compositions that differ profoundly from those of surface waters. This may have important implications for pathways of ice algal carbon acquisition, carbon isotope fractionation as well as for species distribution in the open water phytoplankton.

Dissolved organic matter and nutrients in the Lena River, Siberian Arctic : Characteristics and distribution

Dissolved organic carbon (DOC) and nitrogen (DON), amino acids, carbohydrates and inorganic nutrients were measured on samples taken in July 1994 at 18 stations between Yakutsk and the Lena delta, East Siberia. There were no obvious gradients or features along the river, except in the tributaries, the Aldan and Vilyuy rivers, where significantly higher concentrations of several parameters were measured. Concentrations of DOC varied between 300 and 1000 μM C, with most values varying between 500 and 700 μM C (mean 570 μM C). DON concentrations ranged between 9 and 28 μM N (mean 13 μM N). The C/N ratios of bulk dissolved organic matter (DOM) varied from 30 to 58, with 75% of the values being between 45 and 55 (mean 48). Total dissolved amino acids (TDAA) ranged between 1.6 and 5.4 μM, averaged about 3.5 μM, mostly in the combined form, and represented about 28% of the DON. Free amino acids were only about 2% of TDAA. Glycine, aspartic acid and glutamic acid predominated, accounting for about 41% of TDAA. Total dissolved carbohydrates ranged from 190 to 470 μg glucose equivalents l−1 and averaged 299 μg l−1, forming only 1.2 to 2.5% of the DOC pool. The following ranges of inorganic nutrients were measured: nitrate, 0.01 to 1.4 μM N (mean 0.6 μM N); nitrite, 0.03 to 0.1 μM N (mean 0.07 μM N); ammonium, 0.01 to 0.3 μM N (mean 0.13 μM N); phosphate, 0.2 to 1 μM P (mean 0.5 μM P); silicate, 59 to 87 μM Si (mean 66 μM Si). Carbon isotope data of the suspended organic material suggest that the low inorganic nitrogen values are not due to algal uptake, but rather an inherent characteristic of the river and the catchment area. This, together with positive correlations between silicate, DOC and DON and high C/N values, suggests that the composition of DOM in the Lena River is mainly determined by the input of soil-derived, recalcitrant material and not by autochthonous sources.

Ecology of southern ocean pack ice.

Around Antarctica the annual five-fold growth and decay of sea ice is the most prominent physical process and has a profound impact on marine life there. In winter the pack ice canopy extends to cover almost 20 million square kilometres--some 8% of the southern hemisphere and an area larger than the Antarctic continent itself (13.2 million square kilometres)--and is one of the largest, most dynamic ecosystems on earth. Biological activity is associated with all physical components of the sea-ice system: the sea-ice surface; the internal sea-ice matrix and brine channel system; the underside of sea ice and the waters in the vicinity of sea ice that are modified by the presence of sea ice. Microbial and microalgal communities proliferate on and within sea ice and are grazed by a wide range of proto- and macrozooplankton that inhabit the sea ice in large concentrations. Grazing organisms also exploit biogenic material released from the sea ice at ice break-up or melt. Although rates of primary production in the underlying water column are often low because of shading by sea-ice cover, sea ice itself forms a substratum that provides standing stocks of bacteria, algae and grazers significantly higher than those in ice-free areas. Decay of sea ice in summer releases particulate and dissolved organic matter to the water column, playing a major role in biogeochemical cycling as well as seeding water column phytoplankton blooms. Numerous zooplankton species graze sea-ice algae, benefiting additionally because the overlying sea-ice ceiling provides a refuge from surface predators. Sea ice is an important nursery habitat for Antarctic krill, the pivotal species in the Southern Ocean marine ecosystem. Some deep-water fish migrate to shallow depths beneath sea ice to exploit the elevated concentrations of some zooplankton there. The increased secondary production associated with pack ice and the sea-ice edge is exploited by many higher predators, with seals, seabirds and whales aggregating there. As a result, much of the Southern Ocean pelagic whaling was concentrated at the edge of the marginal ice zone. The extent and duration of sea ice fluctuate periodically under the influence of global climatic phenomena including the El Niño Southern Oscillation. Life cycles of some associated species may reflect this periodicity. With evidence for climatic warming in some regions of Antarctica, there is concern that ecosystem change may be induced by changes in sea-ice extent. The relative abundance of krill and salps appears to change interannually with sea-ice extent, and in warm years, when salps proliferate, krill are scarce and dependent predators suffer severely. Further research on the Southern Ocean sea-ice system is required, not only to further our basic understanding of the ecology, but also to provide ecosystem managers with the information necessary for the development of strategies in response to short- and medium-term environmental changes in Antarctica. Technological advances are delivering new sampling platforms such as autonomous underwater vehicles that are improving vastly our ability to sample the Antarctic under sea-ice environment. Data from such platforms will enhance greatly our understanding of the globally important Southern Ocean sea-ice ecosystem.

Surface properties and processes of perennial Antarctic sea ice in summer

Ice core and snow data from the Amundsen, Bellingshausen, and Weddell Seas, Antarctica show that the formation of superimposed ice and the development of seawater-filled gap layers with high algal standing stocks is typical of the perennial sea ice in summer. The coarse-grained and dense snow had salinities mostly below 0.1 per mil. A layer of fresh superimposed ice had a mean thickness ranging from 0.04-0.12 m. 0.04 to 0.08 m thick gap layers extended downwards from 0.02 to 0.14 m below the water level. These gaps were populated by diatom standing stocks up to 439 µg/l chlorophyll a. We propose a comprehensive heuristic model of summer processes, where warming and the reversal of temperature gradients cause major transformations in snow and ice properties. The warming also causes the re-opening of incompletely frozen slush layers caused by flood-freeze cycles during winter. Alternatively, superimposed ice forms at the cold interface between snow and slush in the case of flooding with negative freeboard. Combined, these explain the initial formation of gap layers by abiotic means alone. The upward growth of superimposed ice above the water level competes with a steady submergence of floes due to bottom and internal melting and accumulation of snow.

Dissolved organic matter in Arctic multi-year sea ice during winter: major components and relationship to ice characteristics

Ice cores were collected between 10.03.93 and 15.03.93 along a 200 m profile on a large ice floe in Fram Strait. The ice was typical of Arctic multi-year ice, having a mean thickness along the profile of 2.56 ±0.53 m. It consisted mostly of columnar ice (83%) grown through congelation of seawater at the ice bottom, and the salinity profiles were characterized by a linear increase from 0 psu at the top to values ranging between 3 and 5 psu at depth. Distributions of dissolved organic carbon (DOC) and nitrogen (DON) and major nutrients were compared with ice texture, salinity and chlorophyll a. DOC, DON, dissolved inorganic nitrogen (DIN), NH4+ and NO2− were present in concentrations in excess of that predicted by dilution curves derived from Arctic surface water values. Only NO3− was depleted, although not exhausted. High DOC and DON values in conjunction with high NH4+ levels indicated that a significant proportion of the dissolved organic matter (DOM) was a result of decomposition/grazing of ice algae and/or detritus. The combination of high NH4+ and NO2− points to regeneration of nitrogen compounds. There was no significant correlation between DOC and Chl a in contrast to DON, which had a positively significant correlation with both salinity and Chl a, and the distribution of DOM in the cores might best be described as a combination of both physical and biological processes. There was no correlation between DOC and DON suggesting an uncoupling of DOC and DON dynamics in multi year ice.

Cyvadic in advanced soft tissue sarcoma: A randomized study comparing two schedules: A study of the EORTC soft tissue and bone sarcoma group

Two hundred forty‐six adults with advanced progressive soft tissue sarcoma received combination chemotherapy with cyclophosphamide, vincristine, Adriamycin (doxorubicin), and DTIC. They were randomly allocated to receive the four drugs simultaneously every 4 weeks (S1: CYVADIC), or pairs of drugs (S2: ADIC‐CYV) alternating at 4 weekly intervals. One hundred sixty‐two patients completed 8 weeks of chemotherapy, and were considered to be evaluable for response. There were 18 complete remissions and 25 partial remissions, an overall response rate of 26%, with a highly significant difference between the two arms in favor of S1 (38% versus 14%, P = 0.001). There were no significant differences between S1 and S2 in terms of median duration of remissions (62 versus 39 weeks), and median survival of responders (85 versus 80 weeks) and of all evaluable patients (43 versus 45 weeks). Karnofsky index (KI) was the single most important prognostic factor. Patients with KI 90–100 showed a remission rate of 41% (56% on the S1 regimen) in contrast with 14% in those with KI 50–80. No patient with a KI of 50 responded to chemotherapy. The main toxicities were nausea, vomiting, anorexia, alopecia and myelosuppression, but did not differ significantly between the two regimens. Our findings suggest that stratification according to KI is essential for studies on chemotherapy for advanced soft tissue sarcomas in order to make a valuable comparison of treatment results.

Productivity, carbon dioxide uptake and net energy return of microalgal bubble column photobioreactors.

This work examined the energy return of Chlorella vulgaris and Dunaliella tertiolecta cultivated in a gas-sparged photobioreactor design where the power input for sparging was manipulated (10, 20, and 50 Wm(-3)). Dry weight, organic carbon and heating values of the biomass were measured, plus a suite of variables including Fv/Fm and dissolved oxygen. A model for predicting the higher heating value of microalgal biomass was developed and used to measure the energetic performance of batch cultivations. High power inputs enhanced maximum biomass yields, but did not improve the energy return. Cultivation in 10 Wm(-3) showed up to a 39% higher cumulative net energy return than 50 Wm(-3), and increased the cumulative net energy ratio up to fourfold. The highest net energy ratio for power input was 19.3 (D. tertiolecta, 12% CO(2), 10 Wm(-3)). These systems may be a sustainable method of biomass production, but their effectiveness is sensitive to operational parameters.

Dissolved organic matter in Antarctic sea ice.

Abstract It has been hypothesized that there are significant dissolved organic matter (DOM) pools in sea-ice systems, although measurements of DOM in sea ice have only rarely been made. The significance of DOM for ice-based productivity and carbon turnover therefore remains highly speculative. DOM within sea ice from the Amundsen and Bellingshausen Seas, Antarctica, in 1994 and the Weddell Sea, Antarctica, in 1992 and 1997 was investigated. Measurements were made on melted sea-ice sections in 1994 and 1997 and in sea-ice brines in 1992. Dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations in melted ice cores were up to 1.8 and 0.78 mM, respectively, or 30 and 8 times higher than those in surface water concentrations, respectively. However, when concentrations within the brine channel/pore space were calculated from estimated brine volumes, actual concentrations of DOC in brines were up to 23.3 mM and DON up to 2.2 mM, although mean values were 1.8 and 0.15 mM, respectively. There were higher concentrations of DOM in warm, porous summer second-year sea ice compared with colder autumn first-year ice, consistent with the different biological activity supported within the various ice types. However, in general there was poor correlation between DOC and DON with algal biomass and numbers of bacteria within the ice. The mean DOC/DON ratio was 11, although again values were highly variable, ranging from 3 to highly carbon-enriched samples of 95. Measurements made on a limited dataset showed that carbohydrates constitute on average 35% of the DOC pool, with highly variable contributions of 1−99%.

Sea ice contribution to the air-sea CO2 exchange in the Arctic and Southern oceans

Although salt rejection from sea ice is a key process in deep-water formation in ice-covered seas, the concurrent rejection of CO2 and the subsequent effect on air–sea CO2 exchange have received little attention. We review the mechanisms by which sea ice directly and indirectly controls the air–sea CO2 exchange and use recent measurements of inorganic carbon compounds in bulk sea ice to estimate that oceanic CO2 uptake during the seasonal cycle of sea-ice growth and decay in ice-covered oceanic regions equals almost half of the net atmospheric CO2 uptake in ice-free polar seas. This sea-ice driven CO2 uptake has not been considered so far in estimates of global oceanic CO2 uptake. Net CO2 uptake in sea-ice–covered oceans can be driven by; (1) rejection during sea–ice formation and sinking of CO2-rich brine into intermediate and abyssal oceanic water masses, (2) blocking of air–sea CO2 exchange during winter, and (3) release of CO2-depleted melt water with excess total alkalinity during sea-ice decay and (4) biological CO2 drawdown during primary production in sea ice and surface oceanic waters.