Interannual Variability in Vertical Export in the Ross Sea: Magnitude, Composition, and Environmental Correlates

Document Type

Article

Publication Date

2-1-2011

Department

Marine Science

School

Ocean Science and Engineering

Abstract

The vertical flux of particulate matter from the surface of the Ross Sea, Antarctica, has been suggested as being large, with substantial seasonal and spatial variations. We conducted a study in which vertical flux was quantified using sediment traps deployed at 200 m and compared to estimates calculated from one-dimensional budgets of nutrients (nitrogen and silicon). Estimates of flux were collected at two locations in the southern Ross Sea from late December to early February during four years: 2001-2002, 2003-2004, 2004-2005, and 2005-2006. Phytoplankton biomass and vertical flux varied substantially seasonally and spatially between the two sites, and among years. The greatest flux was observed in 2001-2002, with a short-term maximum organic carbon flux of 3.13 mmol m-2 d-1, and the summer mean organic carbon flux equal to 0.93 mmol m-2 d-1. In contrast, the mean carbon flux at the same site in 2003-2004 was over an order of magnitude less, averaging 0.19 mmol m-2 d-1, despite the fact that productivity in that year was substantially greater. In 2005-206 the contribution of fecal pellets to flux was smallest among all years, and the pellet contribution ranged from < 1 to more than 50% of organic flux. As the moorings also had surface layer fluorometers, the relationship between surface biomass and sediment trap flux was compared. Temporal lags between surface fluorescence and flux at 200 m maxima in 2003-2004 and 2004-2005 ranged from two to six days; however, in 2005-2006 the temporal offset between biomass and flux was much longer, ranging from 11 to 27 days, suggesting that fecal pellet production appeared to increase the coupling between flux and surface production. Estimates of export from the upper 200 m based on one-dimensional nutrient budgets were greater than those recorded by the sediment traps. Nutrient budgets also indicated that siliceous production averaged ca. 40% of the total annual production. The variations observed in the flux of biogenic matter to depth in the Ross Sea are large, appear to reflect different forcing among years, and at present are not adequately understood. However, such variability needs to be both understood and represented in biogeochemical models to accurately assess and predict the effects of climate change on biogeochemical cycles. (C) 2010 Elsevier Ltd. All rights reserved.

Publication Title

Deep-Sea Research Part I-Oceanographic Research Papers

Volume

58

Issue

2

First Page

147

Last Page

159

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