Late twentieth century increase in northern Spitsbergen (Svalbard) glacier-derived runoff tracked by coralline algal Ba/Ca ratios

Abstract

The Arctic cryosphere is changing rapidly due to global warming. Northern Svalbard is a warming hotspot with a temperature rise of ~ 6 °C over the last three decades. Concurrently, modelled data suggest a marked increase in glacier runoff during recent decades in northern Svalbard, and runoff is projected to increase. However, observational data from before anthropogenic influence are sparse and the potential effects on the surface ocean are unclear. Here, we present a 200-year record of Ba/Ca ratios measured in annual increment-forming coralline algae from northern Spitsbergen as a proxy for past glacier-derived meltwater input. Our record shows a significant increasing trend in algal Ba/Ca ratios from the late-1980s onwards matching modelled regional runoff data, suggesting a drastic increase in land-based runoff. The rate of increase is unprecedented during the last two centuries and captures the impact of amplified warming on the coastal surface ocean in the high Arctic. The algal Ba/Ca runoff proxy offers an opportunity to reconstruct past land-based runoff variability in Arctic settings in high resolution, providing important data for validating and improving climate modelling studies.

Suitability of the Coralline Alga Clathromorphum compactum as an Arctic Archive for Past Sea Ice Cover

“…Barium‐calcium ratios (Ba/Ca) in coralline red algae have previously been used to reconstruct variability in runoff in nearshore environments (Chan et al., 2011). More recently, a study on C. compactum Ba/Ca from Mosselbukta effectively suggested a drastic increase in runoff since the late 1980s (Hetzinger et al., 2021). This could have created more turbidity in the water column and less solar light transmission to the benthos, causing a recent reduction in increment widths in the Mosselbukta samples.…”

‘Ten Years After’—a long‐term settlement and bioerosion experiment in an Arctic rhodolith bed (Mosselbukta, Svalbard)

“…Yet, this is only one facet of the increasing vulnerability of polar rhodolith beds. In Mosselbukta, they have already seen an alarming decline of sea‐ice cover (Hetzinger et al, 2019) along with a marked increase in glacier‐derived runoff (Hetzinger et al, 2021) that increases turbidity. Moreover, future ocean acidification is expected to compromise growth rates and structural integrity of the ecosystem engineer Lithothamnion glaciale (Büdenbender et al, 2011; Ragazzola et al, 2012, 2016; Teichert et al, 2020) and adds to an increase in other human disturbances, such as bottom trawling (Fragkopoulou et al, 2021) and adverse effects of the influx of microplastics into polar waters (Teichert et al, 2021).…”

“…Mosselbukta is located at close to 80° northern latitude, thus the polar night lasts from late October through late February, during which sea ice starts to form that may persist until the early summer (Wisshak et al, 2019: figure 3). Based on a >200‐year geochemical record of Clathromorphum compactum sampled at Mosselbukta, however, local sea ice has been shown to be subject of an alarming decline over the past few decades because of ongoing global ocean warming (Hetzinger et al, 2019), going along with a marked increase in glacier‐derived runoff (Hetzinger et al, 2021).…”

Utility of Dendrochronology Crossdating Methods in the Development of Arctic Coralline Red Algae Clathromorphum compactum Growth Increment Chronology for Sea Ice Cover Reconstruction

“…These programs attempt to statistically mimic the process of visual crossdating by removing long-term trends (low-frequency variability) to isolate the interannual variability, and cross-correlate among individuals to quantify synchrony. Long-term trends, as could be induced by the 20 th century decline of sea ice or increase in glacial runoff (Hetzinger et al, 2019;Hetzinger et al, 2021), or ontogenetic trends, increase the chances of spurious correlations and are therefore eliminated (i.e., detrended). COFECHA flags unusually insignificant correlations as possible errors, prompting the analyst to visually reinvestigate the original samples and/or geochemical data to determine if a true dating error occurred.…”

“…Therefore, reliable highly resolved baseline environmental data required to understand Arctic environments of the past can only be provided by proxy records. The arctic and subarctic coralline red algae species, Clathromorphum compactum, has been used to produce multi-century, annually resolved proxy timeseries of temperature, sea ice, runoff, primary productivity, and multidecadal climate oscillations (Halfar et al, 2008;Halfar et al, 2011;Hetzinger et al, 2011;Halfar et al, 2013;Chan et al, 2017;Hou et al, 2018;Hetzinger et al, 2019;Hetzinger et al, 2021;Leclerc et al, 2021). This species' high-magnesium calcium carbonate skeleton consists of annual calcified growth increments produced at a rate relative to surrounding sea surface temperature (SST) and sunlight access (Williams et al, 2018a) (Figure 1).…”