The vivid red hull of the ship slowly makes its way through the sea ice. What is actually just a few scattered icebergs looks like an ocean of ice to my inexperienced eyes. It is February 2020, north of the Antarctic Peninsula. The scenery is magical although it could be straight out of a black and white old photograph. There are all shades of white around us: the blueish white of the ice, the pure white of the snow, the slightly ivory one of the glaciers and the greyish of the clouds in which they get lost. Sometimes a ray of sunlight breaks through the mist and illuminates a little corner of this immensity, but more usually the whole horizon is shrouded in grey. The entire landscape is that of a polar land, as I had imagined it in my dreams so many times. Everything is like it should be, except for one thing: it does not feel cold. At the beginning of February 2020, the temperature in Hope Bay, where we were sampling at the time, climbs to an all-time record high of 18.3°C, a temperature never recorded before in Antarctica.
Hope Bay on February 3, 2020. Credits: Louise Delhaye.
While the direct consequences of global warming on melting glaciers and rising sea levels are now widely known, in this paper published in Marine Pollution Bulletin last January, we also highlight another side effect of rising temperatures: the potential increase of trace metals in the marine environment.
Trace (or heavy) metals are elements naturally present in small quantities in the environment, and sometimes necessary for the well functioning of organisms. However, if these elements are available in too large quantities, they can become toxic to biota and be a danger to the ecosystem. This is for example the case of arsenic, copper, mercury, cadmium, lead, zinc or chromium.
The objective of this study, which was conducted around the South Shetland Islands, the Bransfield Strait and Hope Bay (Fig. 1), was to establish reference concentration levels of these elements in the surface sediments, a crucial step to enable monitoring in the future. Indeed, the increase in human activities in the north of the Antarctic Peninsula poses a risk of increasing these elements through fuel oil discharges, through the paints used for the hulls of ships and the various discharges linked to scientific stations, among others.
Comparing the values measured during this study with previous measurements in the area, it was observed that there was a general increasing tendency of several heavy metals, particularly regarding chromium.
Figure 1: Illustration of the process by which trace elements are imported into the environment through glacial erosion. Credits: Louise Delhaye.
Our study has, however, highlighted a consistent enrichment of arsenic and copper in the sediments around the South Shetland Islands. The constancy of these values as well as their proximity to runoff input zones suggests that their origin is erosive and would come from the bedrock of these islands rather than from an anthropogenic source. The presence of minerals such as arsenopyrite and basaltic andesite confirms that this bedrock contains arsenic, copper, cadmium and chromium in non-negligible quantities. When glaciers melt, they erode the underlying rocks and bring the elements they contain into the nearby marine environment. Once eroded and deposited in the marine environment, these elements become available to the organisms lower in the food chain. While they may not represent a risk to them, their concentration increases up the trophic chain through the process of biomagnification and becomes more critical to organisms higher up the chain. This means that an increase in the rate of glacier melting in this area could lead in the future to an increase in trace metal concentrations and potentially pose a threat to the ecosystem. However, more data are needed to draw significant conclusions.
To read this study in more details :
Delhaye, L., Elskens, M., Ricaurte-Villota, C., Cerpa, L. and Kochzius, M. (2023). Baseline concentrations, spatial distribution and origin of trace elements in marine surface sediments of the northern Antarctic Peninsula. Marine Pollution Bulletin 187, 114501. https://doi.org/10.1016/j.marpolbul.2022.114501