Calving Event Led to Changes in Phytoplankton Bloom Phenology in the Mertz Polynya, Antarctica

Abstract

Polynyas are subject to variability in winds and ocean circulation and are important sites of ecological productivity. In February 2010, the B09B iceberg collided with the Mertz Glacier Tongue (MGT), calving a 78 × 40-km giant iceberg which modified the icescape and primary productivity of the Mertz polynya. In this study, we use satellite ocean color and sea ice concentration to investigate the variability, trends, and drivers of phytoplankton blooms in the Mertz polynya since 1997. During the bloom, over 21 years, we found (i) a later ice retreat time, (ii) an increase in sea ice concentration, (iii) a decrease in open-water period, (iv) a later bloom start, and (v) a decrease in bloom duration. Our results suggest that major postcalving changes in the physical characteristics of the polynya, mainly its icescape, are the primary drivers of phytoplankton phenology. More specifically, the MGT calving event resulted in significant seasonal and regional changes, with higher eastern chl-a and mean summer chl-a postcalving. While satellite data are useful to study long-term variability in these inhospitable areas, they only focus on the ocean surface and are obscured by ice and clouds. Additional subsurface parameters from seal tags, gliders and moorings in the southernmost polar regions would strengthen our comprehension of phytoplankton and physical changes in ocean dynamics that may have far-reaching consequences, from global circulation to carbon export. Plain Language Summary Polynyas are the most productive areas in the Southern Ocean and play a role in the global oceanic circulation. Evaluating how unexpected and dramatic changes impact biology and chemical cycles in these areas is critical to understand the potential future impact such events may cause on a larger scale. In this paper, we investigated the impact of the calving of a major glacier tongue in the Mertz polynya on the phytoplankton bloom using satellite data. Significant changes happened after the calving event: (i) the bloom duration and open water period time decreased, (ii) the start of the bloom and the retreat of sea ice were delayed, and (iii) the chlorophyll-a (the major phytoplankton pigment which indicates the phytoplankton biomass) and the sea ice concentration increased. These findings show that natural changes can impact the timing of phytoplankton growth that may have consequences for the rest of the ecosystem, from Antarctic krill to baleen whales.

Identifying potential sources of iron-binding ligands in coastal Antarctic environments and the wider Southern Ocean

“…, Liniger et al, 2020). This bloom was confirmed by our in-situ results, where depth integrated Chl-a concentrations reached 68 mg m -2 at the DCM (58 m, Station 17).…”

“…Intense phytoplankton blooms within the Mertz polynya make the region a biological hotspot (McMahon et al, 2002;Sambrotto et al, 2003;Ropert-Coudert et al, 2018) and the production of Dense Shelf Waters via sea-ice formation contributes to a quarter of total Antarctic Bottom Water production (Bindoff et al, 2000Williams et al, 2010;Cougnon et al, 2013). With the calving of the Mertz Glacier Tongue in 2010, this region has already experienced dramatic changes in processes which influence productivity (Tamura et al, 2012;Liniger et al, 2020;Shadwick et al, 2013). Yet the mechanisms underpinning this productivity (such as Fe supply and availability through complexation with ligands) remain elusive.…”

Circumpolar Deep Water and Shelf Sediments Support Late Summer Microbial Iron Remineralization

“…Satellite based observations of ocean color show these fertilization events along coastal regions, from marginal ice zones (Fitch & Moore, 2007), to island wakes (Blain et al., 2007) and polynyas (Arrigo et al., 2015). Coastal marine environments are extremely productive per unit area, sequestering up to 109 g C m −2 yr −1 (Arrigo et al., 2008; Liniger et al., 2020), and support complex food webs (Arrigo et al., 2015; Labrousse et al., 2018). The Mertz Glacier Region (located off the coast of George V and Adelie Land; 140–155°E; Figure 1) is one of the most productive and globally significant regions of the Southern Ocean (Campagne et al., 2015; Sambrotto et al., 2003) and plays a major role in the production of Antarctic Bottom Water to the Australian‐Antarctic Basin (Orsi et al., 2002; Rintoul et al., 1998).…”

Bibliometric analysis of studies of the Arctic and Antarctic polynya

“…The differences between polynya studies in the two polar regions are highlighted by the prosperity of the Antarctic polynya and the slower growth of the Arctic polynya. This can be partly attributed to the heavy shift of the Antarctic ice sheet or glacier in recent years, which is associated with circumpolar polynya (Ciappa and Budillon, 2012;Criscitiello et al, 2013;Stewart et al, 2019;Liniger et al, 2020). Between 1980 and 2021, the Arctic and Antarctic polynya were covered by 47 and 41 web science categories, respectively, with an annual trend of increasing numbers.…”