Interannual variability in vertical export in the Ross Sea: Magnitude, composition, and environmental correlates

Trophic cascades in the western Ross Sea, Antarctica: revisited

“…This hypothesis is consistent with the substantial aggregate fluxes (Asper & Smith 2003) and the large vertical fluxes of organic matter that have been found (Asper & Smith 1999, Collier et al 2000, Smith et al 2011b; nutrient budgets indicate that vertical flux can be as much as 10% of the annual production (Sweeney et al 2000, Smith et al 2011b. Under this scenario, this surplus of ungrazed resources at the base of the trophic web is explained by a depressed abundance of grazers.…”

“…These conclusions about food web structure are consistent with those of Frank et al (2007), who found that 'wasp-waist' food webs predominate in more simple, cold-water continentalshelf ecosystems. Our results suggest that Ross Sea food web models based primarily on bottom-up processes, particularly when dominated by the Phaeocystis-based primary production (Pinkerton et al 2010, Smith et al 2011b, may not adequately capture the most important ecological interactions that have a major structural impact on the upper levels of the food web. Uncoupling between pelagic mesopredators and phytoplankton/primary production was also indicated by Dugger et al (2014), who found no correlation be tween the substantial interannual variations in Ross Sea primary productivity (Arrigo et al 2008, Smith & Comiso 2008 and the productivity and breeding population size of penguins on Ross Island over the past 2 decades.…”

“…One hypothesis to explain the high productivity− low grazer biomass enigma is a trophic cascade in which mesopredators reduce the abundance of middle level organisms, resulting in much of the phytoplankton biomass being ungrazed (Arrigo et al 2003, Ainley 2007, Smith et al 2007, 2011b. This hypothesis is consistent with the substantial aggregate fluxes (Asper & Smith 2003) and the large vertical fluxes of organic matter that have been found (Asper & Smith 1999, Collier et al 2000, Smith et al 2011b; nutrient budgets indicate that vertical flux can be as much as 10% of the annual production (Sweeney et al 2000, Smith et al 2011b.…”

“…Hence, on one hand, diatom production may lead to a 4-level trophic chain composed of primary, secondary and tertiary consumers (diatoms−krill− fish− penguins). On the other hand, the production of colo nial Phaeocystis antarctica, which dominates the phytoplankton during austral spring as well as on an annual basis (Smith et al 2011b), may lead to a shorter trophic chain having only one known macroconsumer (pteropods), with a large portion of the Phaeocystis biomass being microbially remineralized within the water column (Smith et al 2011a). Ainley et al (2006) presented 2 models based on some natural experiments during 8 yr of study at 3 Ross Island Adélie penguin colonies of varying size, thus having co-varying radii of foraging 'halos' extending out from each (see Elliott et al 2009, Ford et al 2014 for a summary of the concept).…”

Role of biogenic silica in the removal of iron from the Antarctic seas

“…Primary production and microbial community composition in this region are variably limited by a number of physical conditions and nutrients, including iron [7][8][9] , which in turn affects biological carbon dioxide uptake and therefore climate 6 . Although these waters are the most productive regions of the Southern Ocean 10 and major sites of atmospheric carbon dioxide uptake 11 , the mechanisms governing the cycling of the limiting nutrient iron are not well understood in these 8 and other ocean areas. On the basis of this gap in knowledge, combined with renewed interest in iron fertilization as an approach to the current climate crisis 12 , an improved understanding of iron cycling in marine systems is critical.…”