Michael Spindler

Ecology of sea ice biota - 2. Global significance

SummaryThe sea ice does not only determine the ecology of ice biota, but it also influences the pelagic systems under the ice cover and at ice edges. In this paper, new estimates of Arctic and Antarctic production of biogenic carbon are derived, and differences as well as similarities between the two oceans are examined. In ice-covered seas, high algal concentrations (blooms) occur in association with several types of conditions. Blooms often lead to high sedimentation of intact cells and faecal pellets. In addition to ice-related blooms, there is progressive accumulation of organic matter in Arctic multi-year ice, whose fate may potentially be similar to that of blooms. A fraction of the carbon fixed by microalgae that grow in sea ice or in relation to it is exported out of the production zone. This includes particulate material sinking out of the euphotic zone, and also material passed on to the food web. Pathways through which ice algal production does reach various components of the pelagic and benthic food webs, and through them such top predators as marine mammals and birds, are discussed. Concerning global climate change and biogeochemical fluxes of carbon, not all export pathways from the euphotic zone result in the sequestration of carbon for periods of hundreds of years or more. This is because various processes, that take place in both the ice and the water column, contribute to mineralize organic carbon into CO2 before it becomes sequestered. Processes that favour the production and accumulation of biogenic carbon as well as its export to deep waters and sequestration are discussed, together with those that influence mineralization in the upper ice-covered ocean.

Ecology of sea ice biota

SummaryPolar regions are covered by extensive sea ice that is inhabited by a variety of plants and animals. The environments where the organisms live vary depending on the structure and age of the ice. Many terms have been used to describe the habitats and the organisms. We here characterize the habitats and communities and suggest some standard terms for them. We also suggest routine sampling methods and reporting units for measurements of biological and chemical variables.

Ecology of sea ice biota - 1. Habitat, terminology, and methodology

SummaryPolar regions are covered by extensive sea ice that is inhabited by a variety of plants and animals. The environments where the organisms live vary depending on the structure and age of the ice. Many terms have been used to describe the habitats and the organisms. We here characterize the habitats and communities and suggest some standard terms for them. We also suggest routine sampling methods and reporting units for measurements of biological and chemical variables.

Implications of brine channel geometry and surface area for the interaction of sympagic organisms in Arctic sea ice

Dynamic temporal and spatial changes of physical, chemical and spatial properties of sea ice pose many challenges to the sympagic community which inhabit a network of brine channels in its interior. Experiments were conducted to reveal the influence of the internal surface area and the structure of the network on species composition and distribution within sea ice. The surface of the brine channel walls was measured via a newly developed method using a fluorogenic tracer. These measurements allowed us to quantify the internal surface area accessible for predators of different sizes, at different ice temperatures and in different ice textures. Total internal surface area ranged from 0.6 to 4 m2 kg−1 ice and declined with decreasing ice temperature. Potentially, 6 to 41% of the area at −2°C is covered by micro-organisms. Cooling from −2 to −6°C drastically increases the coverage of organisms in brine channels due to a surface reduction. A combination of brine channel frequency measurements with an artificial brine network experiment suggests that brine channels ≤200 μm comprise a spatial refuge with microbial community concentrations one to two magnitudes higher than in the remaining channel network. The plasticity of predators to traverse narrow passages was experimentally tested for representative Arctic sympagic rotifers, turbellarians, and nematodes. By conforming to the osmotic pressure of the brine turbellaria match their body dimensions to the fluctuating dimensions of the brine channel system during freezing. Rotifers penetrate very narrow passages several times their body length and 57% their body diameter. In summary, ice texture, temperature, and bulk salinity influence the predatory–prey interactions by superimposing its structural component on the dynamic of the sympagic food web. Larger predators are excluded from brine channels depending on the architecture of the channel network. However, extreme body flexibility allows some predators to traverse structural impasses in the brine channel network.

Distribution and abundance of the planktic foraminifer Neogloboquadrina pachyderma in sea ice of the Weddell Sea (Antarctica)

SummarySea ice cores were obtained from eleven fast ice stations and one floe in the Weddell Sea, Antarctica in January–February 1985. All cores from the north eastern part of the Weddell Sea contained numerous living and dead planktic foraminifers of the species Neogloboquadrina pachyderma (Ehrenberg), while cores drilled in southern parts were barren of foraminifers with one exception. Foraminiferal abundances were variable, with numbers up to 320 individuals per liter melted sea ice. Distribution of foraminifers appears to be patchy, parallel cores taken less than 30 cm apart contained numbers which varied considerably. On the other hand, three cores taken on a transect each more than 3 km apart showed striking similarities. In general, small dead tests were found in the upper parts of the sea ice cores while large living individuals mainly occurred in lower sections. Abundant diatoms probably serve as a food source for the foraminifers. Correlation of foraminiferal abundance with salinity, chlorophyll and nutrient profiles are inconsistent. The possible mechanism of incorporation of N. pachyderma into the ice is discussed.

Morphological and physiological responses ofGlobigerinoides sacculifer (Brady) under varying laboratory conditions

Abstract The planktonic foraminiferGlobigerinoides sacculifer (Brady) was maintained in the laboratory under different temperature (19.5–29.5°C) and salinity (33 and 36‰) regimes. The light and feeding conditions were adjusted to the open ocean environment. The light intensity and quality corresponded to a water depth of 10–30 m and the specimens were fed daily. Specimens were raised from a mean initial size of approximately 220–240 μm to the reproductive mean size ranging from 521 μm to 657 μm according to the different temperature and salinity regimes. The survival time decreased with increasing temperature relatively independent of salinity. The growth rate decreased with decreasing temperatures but significantly only at the lowermost temperature range. The general vitality increased with increasing salinity, partially indicated by more chamber formations of specimens of the 36‰ salinity group in comparison to those of the 33‰ salinity group. The different phenotypes of the final chamber and the different morphologies ofG. sacculifer are discussed.

Life cycle strategy of the Antarctic calanoid copepod Stephos longipes

Abstract Studies on the life strategy of the small calanoid copepod Stephos longipes were carried out in the eastern Weddell Sea during four expeditions (January/February 1985, August 1986, October/December 1986 and April/May 1992). Samples were taken from the water column, the ice/water interface and the sea ice. In winter (August 1986) S. longipes copepodite stage CIV occurred mainly in the upper water layers of the ice covered eastern Weddell Sea, while only nauplii were found in the sea ice. In late winter/early spring (October-December 1986) very low numbers of S. longipes were found in the water column, mainly in the upper 50m, but high numbers occurred immediately below and within the sea ice. Adults dominated in the water column and in the under ice water layer while the sea ice contained nauplii and copepodite stage CI. During summer (January/February 1985) the eastern Weddell Sea was almost entirely free of ice with the exception of fast ice fields atthe ice shelf. During this time S. longipes was concentrated in the upper 50m of the water column and in the ice/water interface where an ice cover was present. Young copepodite stages (CI-CIII) comprised the largest fraction of the population. In autumn (April/May 1992) as new ice began to develop, S. longipes, dominated by copepodite stage CIV, occurred in greatest number within mid-water layers. The abundance of S. longipes in autumn was similar to late winter/early spring highest in the sea ice and lowest in the water column. During all periods of investigation the population structure differed between the various habitats with the youngest population occurring in the sea ice and the oldest in the water column. A younger generation of the S. longipes population appears to overwinter in the sea ice and ice/water interface and an older one in deeper water layers or near the bottom.

Notes on the biology of sea ice in the Arctic and Antarctic

The sea ice which covers large areas of the polar regions plays a major role in the marine ecosystem of both the Arctic and Southern Oceans. Not only do warmblooded animals depend on sea ice as a platform, but the sympagic organisms living internally within the sea ice or at the interfaces ice/snow and ice/water provide a substantial part of the total primary production of the ice covered regions. In addition sea ice organisms are an important food source for a variety of pelagic animals and may initiate phytoplankton spring blooms after ice melt by seeding effects.Sea ice organisms often are enriched by some orders of magnitude if the same volume of melted ice is compared to that of the underlying water column. Three hypotheses try to explain this discrepancy and are discussed. Investigations on the nutrient chemistry within the sea ice system and in-situ observations still are rare. Intense growth of sympagic organisms can result in nutrient deficiencies, at least in selected habitats. Advances in endoscopie methods may lead to a better understanding of the life within the sea ice.

Planktonic foraminiferal ontogeny and new perspectives for micropalaeontology

Planktonic foraminifers are some of the most widely used micro-fossils for dating marine sedimentary rocks and the calcareous test has been used to reconstruct their depositional history over the past 120 million years1. By tracing the successive growth stages of extant representatives of this group, we have obtained criteria which identify pre-adult forms that, traditionally, have been disregarded in foraminiferal research. Thus, large quantities of “… unidentifiable miscellaneous juveniles …”2 have become available to help decipher the fossil record of marine environments. Comparative studies of growth series at species and supraspecific levels allowed the identification of three major species groups, each showing three different developmental stages. Their recognition introduces new possibilities for establishing a natural classification of planktonic foraminifers, for disclosing their evolutionary history and for testing evolutionary models in general.

On the structure and development of Arctic pack ice communities in Fram Strait: A multivariate approach

SummaryThe distribution of ice organisms was investigated in Fram Strait in May 1988 during the ARK V/1 expedition on RV Polarstern. Over a 3 week period the abundances of bacteria, diatoms, auto- and heterotrophic flagellates as well as various groups of meiofauna organisms were observed in the lowermost 30 cm of an ice floe. Data were obtained from three experimental fields under three different light regimes as a result of manipulations of the snow cover. The application of multivariate factor analysis on this time series data set resulted in the characterization of four succession stages of an Arctic sea ice community: 1) the diatom bottom assemblage, 2) the mixed autotrophic assemblage, 3) the mixed auto- and heterotrophic supra-bottom assemblage, and 4) the heterotrophic supra-bottom assemblage. The two most abundant meiofauna groups (Turbellaria, Ciliata) showed different preferences according to algal distribution. While turbellarians were most abundant in samples with mixed populations of diatoms and flagellates, ciliates reached their abundance maxima in samples dominated by diatoms, suggesting different prey selections. We have developed a model for the explanation of the spatial separation of auto- and heterotrophic organisms, highlighting the possible role of DOC production by ice algae and DOC transport with brine flow.