Using Principle Component Analysis to Understand Biogeochemical Cycling of Carbon and Trace Metals in Kongsfjorden, Svalbard

The Arctic Ocean and its coastal areas are especially vulnerable to climate change. Its ecosystem is rapidly changing in response to temperature increase, loss of sea ice, and the combined effects of additional stressors such as freshwater input and legacy pollutants. However, the scientific community currently lacks sufficient information on the mechanisms and drivers behind the biogeochemical cycling of these additional inputs and the consequences that may arise for the Arctic environment.

In July 2020, we collected water samples from the water column of Kongsfjorden (Svalbard, Norway) and from glacier meltwater streams draining into the fjord. The aim of the ongoing study is to understand the mechanism of trace metal and carbon cycling in a polar fjord system that is influenced by meltwater from marine- and land-terminating glaciers. Therefore, filtered water samples (< 0.22 µm) were subject to multi-element analysis via ICP‑MS and measured for further parameters such as alkalinity (AT), dissolved inorganic carbon (DIC) and nutrients. For the subsequent Principle Component Analysis (PCA), 24 variables (e.g. element concentrations) and 14 objects (water column samples of Kongsfjorden) were used to calculate 3 principle components (PCs) with a total explained variance of 88 %. Our results indicate that the PCs can be assigned to distinct distribution patterns and fluxes in the water column along the fjord axis, helping to identify the biogeochemical behavior of single trace metals. We can differentiate between the horizontal mixing of elements with conservative behavior (e.g. Al, Co, Ni, Pb, V and AT), the vertical mixing of nutrient-type elements (e.g. Cd), the mixing of particle-influenced elements at the sediment-water interface (e.g. Fe and Zn) and elements with ambiguous behavior (e.g. Cu, Mn and DIC). Furthermore, we were able to evaluate the influence of different freshwater sources using the source apportionment approach, a statistical method to quantify the importance of various sources on each element’s total burden. The quantitative source contribution reveals two separate signals pointing to glacial meltwater from marine-terminating glaciers vs. freshwater draining through catchment areas and altered by weathering processes. To the best of our knowledge, this is the first data set from the Kongsfjorden region that includes a variety of dissolved trace metals in the water column and was interpreted following extensive statistical analysis. The collected data provides valuable insight into biogeochemical processes and carbon cycling in high-latitude fjord and coastal regions affected by climate change and thus help predict future changes in Arctic ecosystems.

This project has received funding from the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 869383 (ECOTIP).