Temporal variability in benthic-pelagic exchanges: Seasonal cycles, inter-and multiannual variability, and long-term climate change driven trends

Abstract

Exchanges of solutes and solids between the sea floor (benthic) and water column(pelagic) are a vital component of ecosystem functioning in marine habitats around the globe. Various drivers affect these exchanges interdependently, and are in turn affected by them. While some individual driver-process relationships are well known, spatial or temporal ecological context to accurately assess the relative importance of the various drivers, is often missing. The work presented in this thesis explores benthic-pelagic exchange drivers and processes on three different temporal scales. First, short term intra-annual cycling is investigated in a temperate coastal environment. Results showed that there were distinct phases of upward and downward fluxes of significant magnitude throughout the year, in both dissolved and particulate matter fluxes. Timings and cause-effect relationships to direct and indirect drivers however differed between the two. As multi-year climatic influences and the stochastic occurrence of extreme events cause deviation from typical seasonal patterns in the natural environment, the second objective was to characterise medium term inter- and multiannual temporal variability. Decomposition of a decadal temperate time-series data set showed, that the main causes of inter-annual variability were extreme meteorological and biological outlier events, as well as global-scale climatic fluctuations. In order to investigate true long-term temporal variability such as climate change induced trends, the final investigations take place in the Arctic, where the effects of climate change can be observed at a fast pace. Results showed, that there is a clear divide between southern, Atlantic dominated, and northern, Arctic water dominated, environments under present conditions. In the South, there is a net downward flux of dissolved matter and a net upward flux of particulates, while the North exhibits the opposite trend. Based on the driver-process relationships identified in this chapter, it is likely that there will be a change to the dominant direction of seafloor-water exchanges in the northern Barents Sea under future conditions. Overall this thesis provides a novel and fundamental temporal ecological context for important ecosystem processes, evidences the utility of transdisciplinary data analyses and could be used to inform ecosystem models, management decisions, and future studies of similar processes in other environments in the future.

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Identifiers

ORCID for Saskia Ruhl: orcid.org/0000-0002-4650-6045

ORCID for Charlotte Thompson: orcid.org/0000-0003-1105-6838

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