Variability in the freshwater balance of northern Marguerite Bay, Antarctic Peninsula: Results from δ18O

Abstract

We investigate the seasonal variability in freshwater inputs to the Marguerite Bay region (Western Antarctic Peninsula) using a time series of oxygen isotopes in seawater from samples collected in the upper mixed layer of the ocean during 2002 and 2003. We find that meteoric water, mostly in the form of glacial ice melt, is the dominant freshwater source, accounting for up to 5% of the near-surface ocean during the austral summer. Sea ice melt accounts for a much smaller percentage, even during the summer (maximum around 1%). The seasonality in meteoric water input to the ocean (around 2% of the near-surface ocean) is not dissimilar to that of sea ice melt (around 2% in 2002 and 1% in 2003), contradicting the assumption that sea ice processes dominate the seasonal evolution of the physical ocean environment close to the Antarctic continent. Three full-depth profiles of oxygen isotopes collected in successive Decembers (2001, 2002 and 2003) indicate that around 4 m of meteoric water is present in the water column at this time of year, and around 1 m of sea ice formed from this same water column. The predominance of glacial melt is significant, since it is known to be an important factor in the operation of the ecosystem, for example by providing a source of nutrients and modifying the physical environment to control the spatial extent and magnitude of phytoplankton blooms.The Western Antarctic Peninsula is undergoing a very rapid change in climate, with increasing ocean and air temperatures, retreating glaciers and increases in precipitation associated with changes in atmospheric circulation. As climate change continues, we expect meteoric water inputs to the adjacent ocean to rise further. Sea ice in this sector of the Antarctic has shown a climatic decrease, thus we expect a reduction in oceanic sea ice melt fractions if this change continues. Continued monitoring of the oceanic freshwater budget at the western Peninsula is 2 needed to track these changes as they occur, and to better understand their ecological consequences.

Changing distributions of sea ice melt and meteoric water west of the Antarctic Peninsula

“…It was found that meteoric water dominated the freshwater budget overall, accounting for up to 5% of the water in the near-surface layer in summer, whereas seasonal variability in sea ice melt was found to be comparable to that of the meteoric water (around 1-2%) (Meredith et al, 2008a). On interannual timescales, variability in the freshwater fractions was found to be significantly influenced by climatic variability associated with both SAM and ENSO (Meredith et al, 2010).…”

“…At the WAP, we have previously used time series measurements of δ 18 O and salinity from a coastal site in northern Marguerite Bay (close to Rothera Research Station; Figure 1a,b) to document seasonal (Meredith et al, 2008a) and interannual (Meredith et al, 2010) variability in the prevalence of sea ice melt and meteoric water. It was found that meteoric water dominated the freshwater budget overall, accounting for up to 5% of the water in the near-surface layer in summer, whereas seasonal variability in sea ice melt was found to be comparable to that of the meteoric water (around 1-2%) (Meredith et al, 2008a).…”

Freshwater fluxes in the Weddell Gyre: results from δ 18 O

“…Under equilibrium conditions, freezing produces sea ice with an isotopic signature that is only slightly heavier than the seawater from which it derives, with the fractionation factor being of the order of 1.0026-1.0035 [33,34]. Accordingly, concurrent measurements of δ 18 O and salinity at high latitudes are useful in discerning freshwater inputs of isotopically lighter meteoric sources from isotopically heavier sea-ice melt sources [30,35,36].…”

Fossil proxies of near-shore sea surface temperatures and seasonality from the late Neogene Antarctic shelf

“…The north end of Marguerite Bay is covered by winter sea ice for several months, which provides a useful comparison for seasonal meltwater fluxes from sea ice and glacial sources into the modern James Ross Island area, despite different geographical settings. In Marguerite Bay, between 3 and 5% of the near-surface ocean is estimated as formed by glacial meltwater (Jenkins and Jacobs 2008;Meredith et al 2008), with sea ice-melt accounting for a much smaller percentage (ca. 1%) .…”

“…1%) . The effects of seasonal sea ice-melt on the 18 O of seawater, and therefore salinity, are minimal ) but those of glacial ice-melt are considerably more significant as high latitude ice has very low 18 O, with values as low as −50‰ (Weiss et al 1979;Meredith et al 2008). The meltwater fraction that we assume for modern waters around James Ross Island may be a little overestimated because here warm water upwelling onto the shelf (Fahrbach et al 1995) is less significant than in Marguerite Bay, which is affected by upwelling of relatively warm Circumpolar Deep Water (CDW) (e.g., Klinck et al 2004).…”