Takao Hoshiai

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.

Seasonal Variation in Ice Algal Assemblages in the Fast Ice Near Syowa Station in 1983/84

Ice algal assemblages in the fast ice near Syowa Station were investigated from March 1983 to January 1984. Peaks in the standing crop (chlorophyll a) occurred in April–June and October–November; the largest (125 mg chlorophyll a m−2) occurred in mid-November at a site with moderate snow cover. Chlorophyll was most highly concentrated in the bottom of the ice, where the diatoms Amphiprora kufferathii, Berkeleya rutilons, Nitzschia lecointei, N. stellata, N. turgiduloides and Pleurosigma directum were dominant. The chlorophyll concentration within the ice developed mainly in May with little change during the following months at heavily snow-covered sites. Centric diatoms, e.g. Chaetoceros spp., Eucampia antarctica and Rhizosolenia alata were major components in the interior assemblage. The chlorophyll concentration increased in the upper consolidated snow layer during October-January. The dominant species there, Tropidoneis sp., was a minor component of the interior and bottom ice layers. These results suggest that the interior ice algal assemblage was formed by mechanical inclusion of microalgae at the time of sea ice formation, and did not grow in the ice. However, the bottom assemblage grew when irradiance was high enough. The surface assemblage, which was presumed to be inoculated by an interior assemblage through vertical channels, grew in spring.

Diel changes in vertical distribution of Oithona similis (Cyclopoida) and Oncaea curvata (Poecilostomatoida) under sea ice in mid-summer near Syowa Station, Antarctica

The diel vertical distributions of two small copepods, Oithona similis and Oncaeacurvata, were investigated at 4-h intervals over a 24-h period under fast ice near Syowa Station during continuous daylight conditions in the Antarctic mid-summer, December 1993. Oithona similis and O.curvata exhibited small-scale diel vertical migrations during the study period, in a way opposite to what is expected, i.e., remaining mostly in the upper layer during the day and moving into deeper layers at night. The nighttime descent of both species coincided with the time of disappearance of a high algal concentration at the ice–water interface during the day and an increase of the algal concentration in the mid-water layer at night. This suggests the migration behavior of the copepods was responsible for the change of food availability. The daily grazing impact of these copepods was estimated to remove one-third of the algae daily released from ice during mid-summer at Syowa Station.

The Canada-Japan SARES project on the first-year ice of Saroma-ko Lagoon (northern Hokkaido, Japan) and Resolute Passage (Canadian High Arctic)

Abstract A joint Canada-Japan project was conducted on the first-year ice of Saroma-ko Lagoon (northern Hokkaido, Japan) and Resolute Passage (Northwest Territories, Canada) during the winter and spring of 1992. Objectives of the SARES project were to (1) measure the activity of the biological CO 2 pump under the first-year sea ice and (2) characterized its main physical controls. The two study sites exhibit contrasting characteristics. Among others, Saroma-ko Lagoon is the southernmost area in the Northern Hemisphere with seasonal sea ice whereas Resolute Passage is one of the northernmost areas with recurrent first-year sea ice. It was hypothesized that such different characteristics would influence variables that determine the downward flux of biogenic carbon, e.g., hydrodynamics, nutrient replenishment, growth of ice algae and phytoplankton, transfer of primary production to the herbivorous and microbial webs, and sedimentation of biogenic particles. Measured variables included meteorology, hydrodynamics, primary production and nutrient effects, microbial web dynamics, production and grazing of zooplankton and ichthyoplankton, and sedimentation of algae and faecal pellets. The project involved 30 Canadian and 25 Japanese scientists, graduate students and technicians from seven institutions in Canada and twelve in Japan.

Change in habitat of the sympagic copepod Paralabidocera antarctica from fast ice to seawater

Abstract. The occurrence and age structure of an Antarctic ice-associated copepod, Paralabidoceraantarctica, were investigated using a light trap under fast ice near Syowa Station. Sampling was carried out between May and November 1984. P. antarctica were found in high numbers in the traps on 1–2 and 23–24 November. No copepods were found in any trap between May and October. The timing of the absence and occurrence of P. antarctica in the light traps coincided with their ice-dwelling and pelagic life-phases. More than 99% of the total catch was taken in the traps set in the water immediately below the ice in both sampling periods on 1–2 and 23–24 November. The age structure of the P. antarctica populations consisted of copepodite stage III (CIII) to adult and IV (CIV) to adult, respectively. The earlier population was dominated by CIV and CV and the later one by adults. The behavior pattern of P. antarctica is suggested to be controlled by phototactic and thigmotactic traits, and their habitat change from sea ice to seawater may occur by trade-off between two behavioral traits with the acquisition of swimming ability.