Abstract
Warming along the Antarctic Peninsula has led to an increase in the export of glacial meltwater to the coastal ocean. While observations to date suggest that this freshwater export acts as an important forcing on the marine ecosystem, the processes linking ice-ocean interactions to lower trophic-level growth, particularly in coastal bays and fjords, are poorly understood. Here, we identify salient hydrographic features in Barilari Bay, a west Antarctic Peninsula fjord influenced by warm modified Upper Circumpolar Deep Water. In this fjord, interactions between the glaciers and ocean act as a control on coastal circulation, contributing to the redistribution of water masses in an upwelling plume and a vertical flux of nutrients towards the euphotic zone. This nutrient-rich plume, containing glacial meltwater but primarily composed of ambient ocean waters including modified Upper Circumpolar Deep Water, spreads through the fjord as a 150-m thick layer in the upper water column. The combination of meltwater-driven stratification, long residence time of the surface plume owing to weak circulation, and nutrient enrichment promotes phytoplankton growth within the fjord, as evidenced by shallow phytoplankton blooms and concomitant nutrient drawdown at the fjord mouth in late February. Gradients in meltwater distributions are further paralleled by gradients in phytoplankton and benthic community composition. While glacial meltwater export and upwelling of ambient waters in this way contribute to elevated primary and secondary productivity, subsurface nutrient enhancement of glacially-modified ocean waters suggests that a portion of these macronutrients, as well any iron upwelled or input in meltwater, are exported to the continental shelf. Sustained atmospheric warming in the coming decades, contributing to greater runoff, would invigorate the marine circulation with consequences for glacier dynamics and biogeochemical cycling within the fjord. We conclude that ice-ocean interactions along the Antarctic Peninsula margins act as an important control on coastal marine ecosystems, with repercussions for carbon cycling along the west Antarctic Peninsula shelf as a whole.
Highlights
Since 1950, glaciers along the western Antarctic Peninsula (WAP) have undergone rapid change (Cook et al, 2005, 2016), with thinning and acceleration leading to an ice mass loss of 20 Gt yr−1 between 1992 and 2011, a corresponding increase in the export of glacial ice and freshwater to coastal regions, and a contribution to sea-level rise of 0.16 ± 0.06 mm yr−1 (Pritchard and Vaughan, 2007; Rye et al, 2014; Schannwell et al, 2016)
Antarctic Surface Water is evident as a warm and fresh water mass in waters
For the first time, the impact of ice–ocean interactions on the export of meltwater in a WAP fjord, and the physical and biogeochemical ramifications of these processes
Summary
Since 1950, glaciers along the western Antarctic Peninsula (WAP) have undergone rapid change (Cook et al, 2005, 2016), with thinning and acceleration leading to an ice mass loss of 20 Gt yr−1 between 1992 and 2011, a corresponding increase in the export of glacial ice and freshwater to coastal regions, and a contribution to sea-level rise of 0.16 ± 0.06 mm yr−1 (Pritchard and Vaughan, 2007; Rye et al, 2014; Schannwell et al, 2016). Hydrographic sampling has documented the presence of mUCDW along the continental shelf as far north as Flandres Bay, inshore of Anvers Island at 63.3◦S (Figure 1A) (Cook et al, 2016), and noted shoaling and warming of this water mass over the continental shelf over the past 50 years (Martinson et al, 2008; Schmidtko et al, 2014; Couto et al, 2017; Spence et al, 2017). Presence of warm mUCDW along the inner shelf suggests that ocean-driven melting has contributed to changing ice sheet dynamics over the Southern WAP (Wouters et al, 2015; Cook et al, 2016)
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