Mixing of water masses caused by a drifting iceberg affects bacterial activity, community composition and substrate utilization capability in the Southern Ocean

Abstract

The number of icebergs produced from ice-shelf disintegration has increased over the past decade in Antarctica. These drifting icebergs mix the water column, influence stratification and nutrient condition, and can affect local productivity and food web composition. Data on whether icebergs affect bacterioplankton function and composition are scarce, however. We assessed the influence of iceberg drift on bacterial community composition and on their ability to exploit carbon substrates during summer in the coastal Southern Ocean. An elevated bacterial production and a different community composition were observed in iceberg-influenced waters relative to the undisturbed water column nearby. These major differences were confirmed in short-term incubations with bromodeoxyuridine followed by CARD-FISH. Furthermore, one-week bottle incubations amended with inorganic nutrients and carbon substrates (a mix of substrates, glutamine, N-acetylglucosamine, or pyruvate) revealed contrasting capacity of bacterioplankton to utilize specific carbon substrates in the iceberg-influenced waters compared with the undisturbed site. Our study demonstrates that the hydrographical perturbations introduced by a drifting iceberg can affect activity, composition, and substrate utilization capability of marine bacterioplankton. Consequently, in a context of global warming, increased frequency of drifting icebergs in polar regions holds the potential to affect carbon and nutrient biogeochemistry at local and possibly regional scales.

Summer comes to the Southern Ocean: how phytoplankton shape bacterioplankton communities far into the deep dark sea

“…Bacterioplankton communities in surface waters are structured by local competitive effects that favor specializations for effective heterotrophy in the midst of a highly active phytoplankton community, favoring fast-growing copiotrophs that outcompete slow-growing oligotrophic bacteria. These results are consistent with other community structure data from the region (Delmont et al 2014, Kim et al 2014, Richert et al 2015, Dinasquet et al 2017.…”

“…) and dissolved organic compounds (Sipler and Connelly , Dinasquet et al. ), which represent potential substrates for heterotrophic bacteria. Other factors may include irradiance (Bryant and Frigaard , Gómez‐Consarnau et al.…”

Diatoms shape the biogeography of heterotrophic prokaryotes in early spring in the Southern Ocean

“…In contrast, Thalassionema nitzschoides and Chaetoceros curvisetus had strong correlations with OTUs that were previously identified as rapid responders to phytoplankton blooms, as for example the flavobacterial OTUs Polaribacter, Ulvibacter and OTUs from the NS7 group (Buchan et al, 2014). Among these, Polaribacter has frequently been observed in temperate (Teeling et al, 2012;Klindworth et al, 2014;Needham and Fuhrman, 2016) and polar regions under bloom conditions (Williams et al, 2013;Delmont et al, 2014;Luria et al, 2016;Dadaglio et al, 2018) and in response to labile organic matter supply (Dinasquet et al, 2017;Luria et al, 2017;Tada et al, 2017). Similarly, Rhodobacterales had a higher number of strong positive correlations with Thalassionema nitzschoides and Chaetoceros curvisetus than with Fragilariopsis kerguelensis.…”

“…Fragilariopsis kerguelensis was associated to several OTUs of the SAR11 Ia and SAR116 clades and OTUs belonging to OM182 and SAR86, groups that were previously characterized as oligotrophs to be adapted to conditions of low resource supply (Sowell et al, 2009;Yooseph et al, 2010;Swan et al, 2013). Among these, Polaribacter has frequently been observed in temperate (Teeling et al, 2012;Klindworth et al, 2014;Needham and Fuhrman, 2016) and polar regions under bloom conditions (Williams et al, 2013;Delmont et al, 2014;Luria et al, 2016;Dadaglio et al, 2018) and in response to labile organic matter supply (Dinasquet et al, 2017;Luria et al, 2017;Tada et al, 2017). Members of this group are chemolithotrophic (Swan et al, 2011;Sheik et al, 2014) and thus likely better adapted to oligotrophic conditions.…”

Microzooplankton distribution in the Amundsen Sea Polynya (Antarctica) during an extensivePhaeocystis antarcticabloom

“…Inversely, salinity increased with decreasing latitude and proximity to the sea ice surrounding the polynya. Two stations along transect 2 deviated from this pattern; St. 57.21 where the upper ~100 m was mixed as it was located in the wake of a drifting iceberg (Randall-Goodwin et al, 2015; Dinasquet et al, 2017), and St. 35 characterized by high surface temperatures. Detailed information on the hydrography is presented elsewhere (Randall-Goodwin et al, 2015; Yager et al, 2016).…”