Seasonal copepod lipid pump promotes carbon sequestration in the deep North Atlantic

Physical, chemical and biological processes can mediate carbon transfer from surface ocean waters to below the permanent pycnocline and so promote ocean carbon sequestration. Passive sinking of organic and carbonate-rich biogenic particles - the ‘biological pump’ -has been estimated to account for a sequestration flux of 2 - 8 gC m-2 yr-1 at around 1000m depth. Here we identify a comparably important mechanism for sequestering carbon in the North Atlantic and other sub-polar seas. We estimate that as a result of the annual vertical migration of overwintering copepods, between 2 and 6 gC m-2 yr-1 are actively transported to below the permanent pycnocline as lipids. Only 25 - 50% of these lipids are carried back to the surface in spring with the surviving copepods, resulting in a sequestration flux of 1 to 4 gC m-2 yr-1. This ’lipid pump’ has gone largely un-recorded in either direct measurements of carbon sequestration, or estimates based on surface production and export flux. In addition, elemental ratios of nitrogen, phosphorus, silicon and iron to carbon are extremely low or zero in lipids, so the lipid pump does not strip the surface ocean of limiting nutrients, and decouples the carbon sink from nutrient replenishment rates

Concentration of mercury and other metals in an Arctic planktonic food web under a climate warming scenario

Arctic marine ecosystems act as a global sink of mercury (Hg) and other metals, and high concentrations of these have been measured in higher trophic-level organisms. Nevertheless, the concentrations of metals at the basis of the marine food web in the Arctic is less known despite the likelihood of biomagnification from dietary sources. We investigated the concentrations of mercury (Hg) and other metals in different size fractions of plankton in West Greenland. All size fractions contained detectable levels of Hg (ranging from 4.8 to 241.3 ng g dw− 1 ) at all stations, although with high geographic variability, likely reflecting the sources of mercury (e.g., meltwater). In many cases, the concentrations in the larger-size fractions were lower than in the smaller-size fractions, suggesting depuration through the metabolic activity of mesozooplankton. Concentrations of Cd, Pb, V, Ni, and Cr were higher than previously reported elsewhere in the Arctic

Comparative ecology of over-wintering Calanus finmarchicus in the northern North Atlantic, and implications for life-cycle patterns

Data from plankton net and Optical Plankton Counter sampling during 12 winter cruises between 1994 and 2002 have been used to derive a multi-annual composite 3-D distribution of the abundance of over-wintering Calanus finmarchicus in a swath across the North Atlantic from Labrador to Norway. Dense concentrations occurred in the Labrador Sea, northern Irminger Basin, northern Iceland Basin, eastern Norwegian Sea, Faroe–Shetland Channel, and in the Norwegian Trench of the North Sea. A model of buoyancy regulation in C. finmarchicus was used to derive the lipid content implied by the in situ temperature and salinity at over-wintering depths, assuming neutral buoyancy. The Faroe–Shetland Channel and eastern Norwegian Sea emerged as having the highest water column-integrated abundances of copepodites, the lowest over-wintering temperature, and the highest implied lipid content. The results are discussed in the context of spatial persistence of populations, seasonal patterns of abundance, and relationships between over-wintering and lipid accumulation in the surface waters