Distribution and biomass transport of ice amphipods in drifting sea ice around Svalbard

Diversity and distribution of ice amphipods were determined in drifting sea ice around Svalbard during May–August 2003–2005. Sea-ice concentrations were determined visually and by satellite recordings. Backward trajectories for ice drift, based on satellite observations, indicated that multi-year ice in the area had originated 3–5 years earlier in the Kara Sea and western Laptev Sea, whereas some of the younger ice (1–2 years) may have originated in Franz Josef Land area. Quantitative collections of ice amphipods were obtained by SCUBA divers from flat areas and ridges below sea ice. The abundance and biomass were generally higher on ridges, particularly for the large Gammarus wilkitzkii, whereas Apherusa glacialis was more abundant on flat areas. Abundance and biomass varied among seasons (May–August) and years, with low values in May and higher values in July. The high values were similar to abundance and biomass values from July 1996. Redundancy analysis showed that 33% and 52% of the variability in respective species abundance and biomass could be explained by environmental variables, with ice draft and snow cover being the most important. erall mean biomass for flats (0.30±0.05 g m−2) and ridges (1.64+0.46 g m−2) were used to calculate ice-associated biomass transport based on revised mean annual ice flux through Fram Strait (662,000 km2 yr−1) and into the Barents Sea (total 228,000 km2 yr−1). About 478×103 t WW (57×103 t C) of ice amphipods are transported annually through Fram Strait and 194×103 t WW (23×103 t C) into the northern Barents Sea, implying that 71% of the amphipod biomass in drifting sea ice passes through Fram Strait and 29% enters the Barents Sea. Climate induced reduction in ice thickness and extent will likely decrease this southward biomass transport, and thus the current carbon input of about 80×103 t C yr−1 into these marginal seas. Ice amphipod populations probably cannot be sustained if the summers become ice free in the Arctic Ocean, and particularly reduction of multi-year ice in the Arctic Ocean will affect long-lived species such as Gammarus wilkitzkii.