Abstract
The Ross Sea is one of the most productive areas of the Southern Ocean and includes several functionally different marine ecosystems. With the aim of identifying signs and patterns of microbial response to current climate change, seawater microbial populations were sampled at different depths, from surface to the bottom, at two Ross Sea mooring areas southeast of Victoria Land in Antarctica. This oceanographic experiment, the XX Italian Antarctic Expedition, 2004-05, was carried out in the framework of the ABIOCLEAR project as part of LTER-Italy. Here, microbial biogeochemical rates of respiration, carbon dioxide production, total community heterotrophic energy production, prokaryotic heterotrophic activity, production (by3H-leucine uptake) and prokaryotic biomass (by image analysis) were determined throughout the water column. As ancillary parameters, chlorophylla, adenosine-triphosphate concentrations, temperature and salinity were measured and reported. Microbial metabolism was highly variable amongst stations and depths. In epi- and mesopelagic zones, respiratory rates varied between 52.4–437.0 and 6.3–271.5 nanol O2l-1h-1; prokaryotic heterotrophic production varied between 0.46–29.5 and 0.3–6.11 nanog C l-1h-1; and prokaryotic biomass varied between 0.8–24.5 and 1.1–9.0 µg C l-1, respectively. The average heterotrophic energy production ranged between 570 and 103 mJ l-1h-1in upper and deeper layers, respectively. In the epipelagic layer, the Prokaryotic Carbon Demand and Prokaryotic Growth Efficiency averaged 9 times higher and 2 times lower, respectively, than in the mesopelagic one. The distribution of plankton metabolism and organic matter degradation was mainly related to the different hydrological and trophic conditions. In comparison with previous research, the Ross Sea results, here, evidenced a relatively impoverished oligotrophic microbial community, throughout the water column.
Highlights
The present work aims to explore the carbon fate through microbes in an area of the Ross Sea (RS) and to identify signs and patterns of microbial responses to current climate change.The Southern Ocean (SO) plays an important role in world climate since it is considered the engine of the worldwide oceanic currents
At the 200 m depth-horizon, temperature showed a wedge of relatively warm water, with temperatures ranging from -1.3 to -0.7 °C, that had crept between two cooler water masses, with temperatures ranging from -1.9 to -1.3 °C
This study was carried out within a time series of research conducted since the nineties in the Ross Sea
Summary
The present work aims to explore the carbon fate through microbes in an area of the Ross Sea (RS) and to identify signs and patterns of microbial responses to current climate change. The Southern Ocean (SO) plays an important role in world climate since it is considered the engine of the worldwide oceanic currents. The annual pelagic primary production is largely confined to this period, when light and nutrient conditions are favourable for the phytoplankton growth. An early spring retreat of sea ice, along with a decrease in seasonal sea-ice cover, an increase of light availability and a presumed constraint on primary production, has been reported (Dinasquet et al 2018, Constable et al 2014). The low iron-limited primary productivity ensures that SO falls into a high-nutrient low-chlorophyll (HNLC) type of environment (Minas et al 1986, Dinasquet et al 2018, Deppler and Davidson 2017)
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