Exceptional 20th Century Shifts in Deep-Sea Ecosystems Are Spatially Heterogeneous and Associated With Local Surface Ocean Variability

Abstract

Traditionally, deep-sea ecosystems have been considered to be insulated from the effects of modern climate change, but with the recognition of the importance of food supply from the surface ocean and deep-sea currents to sustaining these systems, the potential for rapid response of benthic systems to climate change is gaining increasing attention. However, very few ecological time-series exist for the deep ocean covering the twentieth century. Benthic responses to past climate change have been well-documented using marine sediment cores on glacial-interglacial timescales, and ocean sediments have also begun to reveal that planktic species assemblages are already being influenced by global warming. Here, we use benthic foraminifera found in mid-latitude and subpolar North Atlantic sediment cores to show that, in locations beneath areas of major surface water change, benthic ecosystems have also changed significantly over the last ∼150 years. The maximum benthic response occurs in areas which have seen large changes in surface circulation, temperature, and/or productivity. We infer that the observed surface-deep ocean coupling is due to changes in the supply of organic matter exported from the surface ocean and delivered to the seafloor. The local-to-regional scale nature of these changes highlights that accurate projections of changes in deep-sea ecosystems will require (1) increased spatial coverage of deep-sea proxy records, and (2) models capable of adequately resolving these relatively small-scale oceanographic features.

A blueprint for integrating scientific approaches and international communities to assess basin-wide ocean ecosystem status

“…For example, an analysis of a citizen-science catalogue of humpback whale (Megaptera novaeangliae) tail fluke images standardised by survey efforts suggests that whale abundance in Bermuda's waters increased linearly since 2011, and varied from ~790 individuals in 2016 to ~1400 in 2020 52,53 56 , for example, were able to demonstrate the importance of changes in food flux for the rise and fall of these ecosystems in the Atlantic. O'Brien et al 57 used benthic foraminifera from mid-latitude and subpolar North Atlantic sediment cores to show strong shifts in benthic ecosystems over the last ~150 years, with peak responses occurring in areas that experienced large changes in surface circulation, temperature, and/or productivity. (5) Ancient environmental DNA (aDNA) uses eDNA methods and metabarcoding on sediment cores to reproduce temporal changes in pelagic plankton.…”

An Outlook for the Acquisition of Marine Sedimentary Ancient DNA (sedaDNA) From North Atlantic Ocean Archive Material

“…Subsequently, changes in oceanographic conditions have been linked to alterations in biological communities of the North Atlantic. Measurements and reconstruction of salinity, nitrates, wind, water circulation and available nutrients have been associated with variability in marine biota (Boyd & Hutchins, 2012), including both planktonic and benthic species (Barton et al, 2016;Hátún et al, 2016Hátún et al, , 2009Henson et al, 2009;O'Brien et al, 2021;Osman et al, 2019). Predictions on future Atlantic ocean conditions indicate that temperature redistributions and slowing of the AMOC will likely cause diatom and dinoflagellate communities (important planktonic primary producers) to shift northwards (Barton et al, 2016).…”

“…Traditionally, variations in oceanographic conditions and marine biological communities have been derived from the analyses of microfossils preserved in sediments (Yasuhara et al., 2020). For example, microscopy analyses of fossilized eukaryotes, such as diatoms, foraminifera, dinoflagellate cysts, radiolaria, and coccolithophores (all belonging to the large group of single‐celled protists) have been the gold standard to reconstruct paleoenvironments, paleoproductivity and palaeoceanographic conditions (Mudie et al., 2006; O’Brien et al., 2021; Oksman et al., 2019; Weckström et al., 2020; Yasuhara et al., 2020). However, such microfossil‐based reconstructions are limited, as only the more robust and fossilized species are preserved in seafloor sediments, meaning that the vast number of soft‐bodied organisms that have also thrived in the past ocean are not accounted for (e.g., many flagellates, chlorophytes, haptophytes, ciliates, zooplankton) (Ellegaard et al., 2020; Witkowski et al., 2016).…”

Tidal to decadal scale hydrodynamics at two contrasting cold-water coral sites in the Northeast Atlantic

“…The AMOC phases and other changes in the North Atlantic gyre system cause a cascade of effects across all trophic levels of the North Atlantic upper water ecosystems (Hátún et al, 2009a) including important commercial fish stocks (Hátún et al, 2009) and seabirds (Hátún et al, 2017). Changes in the basin-scale circulation and water mass properties propagate to the deep sea and may affect ecosystem processes in different ways (Puerta et al, 2020;Morato et al, 2020;O'Brien et al, 2021). Several studies have highlighted linkages between alternating phases of ocean current systems to long-term changes in the growth rates and elemental composition of CWC reefs during Holocene (e.g., Montero-Serrano et al, 2011;Dubois-Dauphin et al, 2019).…”