The optical and biological properties of glacial meltwater in an Antarctic fjord

Abstract

As the Western Antarctic Peninsula (WAP) region responds to a warmer climate, the impacts of glacial meltwater on the Southern Ocean are expected to intensify. The Antarctic Peninsula fjord system offers an ideal system to understand meltwater’s properties, providing an extreme in the meltwater’s spatial gradient from the glacio-marine boundary to the WAP continental shelf. Glacial meltwater discharge in Arctic and Greenland fjords is typically characterized as relatively lower temperature, fresh and with high turbidity. During two cruises conducted in December 2015 and April 2016 in Andvord Bay, we found a water lens of low salinity and low temperature along the glacio-marine interface. Oxygen isotope ratios identified this water lens as a mixture of glacial ice and deep water in Gerlache Strait suggesting this is glacial meltwater. Conventional hydrographic measurements were combined with optical properties to effectively quantify its spatial extent. Fine suspended sediments associated with meltwater (nanoparticles of ~ 5nm) had a significant impact on the underwater light field and enabled the detection of meltwater characteristics and spatial distribution. In this study, we illustrate that glacial meltwater in Andvord Bay alters the inherent and apparent optical properties of the water column, and develop statistical models to predict the meltwater content from hydrographic and optical measurements. The predicted meltwater fraction is in good agreement with in-situ values. These models offer a potential for remote sensing and high-resolution detection of glacial meltwater in Antarctic waters. Furthermore, the possible influence of meltwater on phytoplankton abundance in the surface is highlighted; a significant correlation is found between meltwater fraction and chlorophyll concentration.

Species Distribution Modeling Predicts Significant Declines in Coralline Algae Populations Under Projected Climate Change With Implications for Conservation Policy

“…However, our results do not predict this kind of range shift to be available for non-geniculate coralline algae because of light limitation. Increased Arctic melt-water introduction (Pan et al, 2019), may enable a downward expansion or movement of non-geniculate coralline algae populations due to clearing of the water column. If this was to occur, there would also be knock-on implications for the biodiversity associated with this habitat, which may be depth limited or increased light penetration may lead to macroalgae overgrowth.…”

Investigation of Sediment-Rich Glacial Meltwater Plumes Using a High-Resolution Multispectral Sensor Mounted on an Unmanned Aerial Vehicle

“…The analysis of turbidity or similar measures for the identification of glacial discharges was previously described in studies in both the Arctic and Antarctic regions [19,64,65]. However, combining it with remote sensing methods is less common in the Antarctic [66].…”

Variability of Sediment Accumulation Rates in an Antarctic Fjord

“…(2) increased turbidity and a reduction in fjord productivity (e.g., Grange & Smith, 2013;Pan et al, 2019); (3) decreased total and relative biogenic sediment production; and (4) increased burial disturbance, leading to reduced benthic diversity and abundance.…”

“…Wind events mix fjord waters and drive circulation (Lundesgaard, Powell, et al, ). Seasonal plankton blooms can be intense and cause decreased light transmission in surface waters, especially in the middle basins (Pan et al, ). Recent studies indicate large values for summer biomasses of krill and humpback whales (Espinasse et al, ; Nowacek et al, ) as well as high abundances and biodiversity of fjord megabenthos on soft sediments and dropstones (Grange et al, ; Grange & Smith, ; Ziegler et al, ).…”

“…Suspended sediment concentrations are weak (<6 mg/L) within intermediate nepheloid layers, or "cold tongues," which extend up to 6 km from ice fronts at multiple water depths (Domack & Ishman, 1993;Pan et al, 2019). These layers are postulated to form by tidal pumping of seawater into a gap between the terminus and the bed, causing resuspension of sediment (Domack & Williams, 1990), or by variable subglacial meltwater discharge (Domack et al, 1994).…”