Meltwater Discharge From Marine‐Terminating Glaciers Drives Biogeochemical Conditions in a Greenlandic Fjord

Abstract

An increasing body of work has shown the potential impacts of subglacial discharge from marine‐terminating glaciers on the marine environment around Greenland. Upwelling of nutrients associated with rising buoyant plumes near the front of marine‐terminating glaciers plays a key role in maintaining the high productivity of connected fjords. The response of protist communities to subglacial discharges into fjords nevertheless remains poorly understood. Here we show data of water properties, nutrients, and protist communities during two summers in 2018 and 2019 in a Greenlandic fjord system fed by marine‐terminating glaciers. This study included the period of intense summer melting of the Greenland Ice Sheet in 2019. The data revealed high nutrient concentrations in 2019 that were attributed to intensified upwelling of nutrients and dissolved iron into the subsurface layer. The source of the iron and the nutrients was subglacial discharge and deep fjord water, respectively. Intense glacial discharges in 2019 mitigated nitrate and phosphate limitations of phytoplankton in the fjord and resulted in an increase of chlorophyll a in the subsurface layer and growth of large diatoms. Heterotrophic protists such as dinoflagellates, tintinnids, and nanoflagellates were more abundant in the summer of 2019. We concluded that nutrient upwelling by subglacial discharges was the major driver of the structure of lower trophic levels in fjord ecosystems. We hypothesize that the more intense melting of glaciers and related increase in subglacial discharge will enhance nutrient upwelling, and increased summer productivity in fjords until the glaciers retreat and terminate on land.

Glacier retreat alters downstream fjord ecosystem structure and function in Greenland

“…1). In Nuup Kangerlua with marine-terminating glaciers, larger phytoplankton (>5 µm) remain abundant and metabarcoding data reveal the continuous presence of Bacillariophyta (diatoms) as observed in a North Greenland fjord 4 . Chlorophyll a in the photic zone is higher and primary production measurements show rates of ~200 to ~800 mgC m −3 d −1 from June to August (Fig.…”

Climate Variability and Glacier Dynamics Linked to Fjord Productivity Changes Over the Last ca. 3300 Years in Nuup Kangerlua, Southwest Greenland

“…Ocean heat fluxes are important drivers of glacial melt (Bendtsen et al., 2015) and the mild oceanic and atmospheric conditions likely promoted glacial melt at the time leading to enhanced productivity. In fjords with marine‐terminating glaciers, summer productivity has been linked to subglacial meltwater discharge that provides critical upwelling of nutrient‐rich deep‐water (e.g., Kanna et al., 2022; Meire et al., 2017). Presently, summer blooms in Nuup Kangerlua account for a significant fraction (35%–40%) of the annual production, that was estimated to be up to 120 g C m −2 year −1 in 2013 (Juul‐Pedersen et al., 2015; Meire et al., 2015).…”

Rubisco in high Arctic tidewater glacier‐marine systems: A new window into phytoplankton dynamics

“…Across the Arctic, nitrate delivery by tidewater glacial marine systems has been tied to higher primary production using in situ chlorophyll a (Chl a ) measurements, carbon fixation rate estimates, and remote sensing analyses (Meire et al 2017; Vonnahme et al 2021; Dunse et al 2022), but there have been very few studies evaluating the impact of tidewater glaciers on marine phytoplankton community dynamics (Kanna et al 2022; Maselli et al 2023). Despite the high density of tidewater glaciers across Nunavut in the Canadian Arctic Archipelago, there have been no comprehensive studies investigating interactions between phytoplankton and glaciers in this region.…”