Physiological state of phytoplankton communities in the Southwest Atlantic sector of the Southern Ocean, as measured by fast repetition rate fluorometry

Abstract

The majority of the Southern Ocean is a high-nutrient low-chlorophyll (HNLC) ecosystem. Localized increases in chlorophyll concentration measured in the wake of bathymetric features near South Georgia demonstrate variations in the factors governing the HNLC condition. We explore the possibility that the contrast between these areas of high-chlorophyll and surrounding HNLC areas is associated with variations in phytoplankton photophysiology. Total dissolvable iron concentrations, phytoplankton photophysiology and community structure were investigated in late April 2003 on a transect along the North Scotia Ridge (53–54°S) between the Falkland Islands and South Georgia (58–33°W). Total dissolvable iron concentrations suggested a benthic source of iron near South Georgia. Bulk community measurements of dark-adapted photochemical quantum efficiency (F v/F m) exhibited a sharp increase to the east of 46°W coincident with a decrease in the functional absorption cross-section (sPSII). Phytoplankton populations east of 46°W thus displayed no physiological symptoms of iron or nitrate stress. Contrasting low F v/F m west of 46°W could not be explained by variations in the macronutrients nitrate and silicic acid and may be the result of taxon specific variability in photophysiology or iron stress. We hypothesize that increased F v/F m resulted from local relief from iron-stress near South Georgia, east of Aurora Bank, an area previously speculated to be a “pulse point” source of iron. Our measurements provide one of the first direct physiological confirmations that iron stress is alleviated in phytoplankton populations near South Georgia

Sedimentary and atmospheric sources of iron around South Georgia, Southern Ocean: a modelling perspective

“…As previously measured around South Georgia (Nielsdóttir et al, 2012, Holeton et al, 2005, but also in other regions of the Southern Ocean (e.g. Ardelan et al, 2010;Bucciarelli et al, 2001;Planquette et al, 2007), the model depicts highest dFe concentrations in near-shore waters (> 5 nM), decreasing with distance from the island.…”

Vulnerability of Antarctic shelf biodiversity to predicted regional warming

“…The wide depth span of many species means that even at 1 geographic location the range of temperatures across depths may be significant (see e.g. Holeton et al 2005). Shortly after the 1967 to 1970 eruptions at Deception Island, Gallardo et al (1977) reported a progression of species returning to the caldera, despite being patchily very warm and chemically altered.…”

Nitrous oxide variability at sub-kilometre resolution in the Atlantic sector of the Southern Ocean

“…Extensive phytoplankton blooms were observed in the vicinity of South Georgia and across the Scotia Sea, extending to the southern limit of the Polar Front (Korb et al, 2004(Korb et al, , 2005. These blooms can develop due to a stable water column over the shelf and iron input from 10 the shelf sediments and island runoff (de Baar et al, 1995;Holeton et al, 2005;Korb et al, 2005;Wadley et al, 2014). This accumulation of biomass would supply ample substrate to sustain high nitrification rates and N 2 O production could lead to the observed supersaturating close to the island.…”