Impact of bottom water currents on benthic foraminiferal assemblages in a cold-water coral environment: The Moira Mounds (NE Atlantic)

Abstract

Strong bottom currents play a key role in cold-water coral environments by shaping their morphology and providing the necessary food for the corals to thrive. This study investigates the differences between living and dead benthic foraminiferal assemblages in such environments, more precisely on the Moira Mounds (NE Atlantic). A specific focus is to understand the role of currents and their influence on the taphonomy of benthic foraminiferal assemblages. Here, we analyze high-resolution sediment grain size distributions coupled with benthic foraminiferal assemblage composition to assess how much deep-sea bottom currents affect benthic foraminiferal assemblages. We suggest that the dead benthic foraminiferal assemblage consists of a reworked glacial fauna associated with contemporary species. Reworked glacial species (Elphidium excavatum, Sigmoilopsis schlumbergeri) are the most abundant. Dominant species that are present almost exclusively in the living assemblage (Alabaminella weddellensis, Nonionella iridea, Trifarina spp.) are associated with high phytodetritus input, possibly as a response to the later phase of the North-east Atlantic spring bloom. Dead assemblages are further characterized by the scarcity of organic-walled agglutinated foraminifera in comparison to living assemblages. Sediment grain size distributions show that the downslope Moira Mounds consist of well-sorted fine sand, typical of contourite deposits in the area. Grain size distributions and the average Shannon diversity of living and dead foraminiferal assemblages indicate that the coral cover offers a sheltered environment, baffling eroded sediment and preventing post-mortem transport of dead foraminifera. We conclude that cold-water coral environments provide a valuable paleoenvironmental archive by trapping sediment in an otherwise non-depositional system.

Cold-Water Coral Mound Archive Provides Unique Insights Into Intermediate Water Mass Dynamics in the Alboran Sea During the Last Deglaciation

“…As all Bolivinid species (Bolivina alata, B. difformis, B. dilatata, B. pseudoplicata, B. pseudopunctata, B. spathulata, B. striatula and B. variabilis) follow the same distribution pattern throughout FIGURE 2 | Stratigraphy, core description and macrofaunal content of core MD13-3455G. The core descriptions and macrofaunal content were previously reported by Feenstra (2020). The stratigraphy is constructed by combining the G. bulloides planktonic (light blue curve) and C. lobatulus benthic (dark blue curve) δ 18 O records ( VPDB), U/Th coral and calibrated median 14 C foraminifera ages (Tables 1, 2).…”

“…This general warming at shallow and intermediate water depths is associated to a shift in the coral community, M. oculata becoming the dominant species instead of D. pertusum, and in the benthic foraminiferal assemblage (Figure 2). This change from D. pertusum to M. oculata dominated environments is documented at a number of different areas in the East and West Melilla Coral Provinces (Fink et al, 2013(Fink et al, , 2015Stalder et al, 2015Stalder et al, , 2018Wang et al, 2019;Feenstra, 2020), and is hence a widespread phenomenon. The decrease in sortable silt mean grain size together with the retreat of the epibenthic foraminifera species C. lobatulus indicates that the seafloor experienced a decrease in bottom current strength during the Holocene.…”

“…The upper part of the core, corresponding to GI-1 and the Holocene, consists of framework building scleractinian CWCs (D. pertusum and M. oculata) embedded in a matrix of mixed, clay to silt sized carbonate/siliciclastic material (Figure 2; Feenstra, 2020). Sedimentary and macrofaunal variations observed in core MD13-3455G are reported in more detail by Feenstra (2020).…”

“…The recent (last 20 ka) history of coral proliferation of the East Melilla Coral Province has been documented by a number of studies in the past years (Fink et al, 2013(Fink et al, , 2015Stalder et al, 2015Stalder et al, , 2018Wang et al, 2019;Feenstra, 2020). The conclusions drawn from these different studies indicate that corals experienced their most intense recent proliferation phase during Greenland Interstadial 1 (GI-1) and during the Early Holocene, whilst coral growth was reduced or halted during the Mid to Late Holocene, Younger Dryas and Last Glacial Maximum.…”

The influence of Atlantic climate variability on the long-term development of Mediterranean cold-water coral mounds (Alboran Sea, Melilla Mound Field)

“…Eisele et al, 2011). Indeed, the baffling effect of coral framework can locally reduce bottom current velocity and favour the deposition of fine sediments (Huvenne et al, 2009;Titschack et al, 2009;Fentimen et al, 2020), thus leading to an underestimation of ̅̅̅ during periods with high CWC content. Because of this, only relative 210 increases in ̅̅̅ are considered in combination with results obtained from other proxies.…”