Zoophycos in deep‐sea sediments indicates high and seasonal primary productivity: Ichnology as a proxy in palaeoceanography during glacial–interglacial variations

Abstract

Trace fossils provide valuable palaeoenvironmental information in hemipelagic settings. This is particularly true in the case of Zoophycos, an easily recognizable trace fossil in core. At IODP site U1385, Zoophycos was found throughout an interval representing 1.5 Ma, covering 45 glacial–interglacial cycles mediated by obliquity (41 ka) and short‐term eccentricity (100 ka). Zoophycos is most common in sediments deposited during glacial times and when the sedimentation rate was intermediate and primary production was high and seasonal. Occurrences of Zoophycos elsewhere support a similar relationship with seasonal organic‐matter deposition. This is particularly significant considering that seasonality of organic‐matter deposition is difficult to decipher from the sediment record. Zoophycos appears to represent a useful proxy to characterize high and seasonal organic‐matter deposition and primary productivity in Neogene hemipelagic deposits.

Site U1500

“…The occurrence of trace fossil assemblages or even a single ichnogenus in deep-sea sediments can provide information about the depositional environment. They have been increasingly used as paleoceanographic tools to infer the sedimentary and ecological setting (e.g., Knaust and Bromley, 2012;Dorador et al, 2016).…”

“…In Cenozoic hemipelagic sediments, the presence of Zoophycos is used to interpret deep-sea environmental conditions related to energy variation, sedimentation rate change, and food availability (e.g., Löwemark, 2015). A study from Site U1385 on the West Iberian margin shows that Zoophycos is most common in sediments deposited during glacial times, when the sedimentation rate was intermediate and primary production was high and seasonal, suggesting a relationship with seasonal organic matter deposition (Dorador et al, 2016). Zoophycos was frequently observed in dark reddish gray calcareous-rich claystone in Subunit VB (Figure F22D).…”

Lateral variability of ichnological content in muddy contourites: Weak bottom currents affecting organisms’ behavior

“…Zoophycos is a deep tier structure with several ethological interpretations, but consensus favors the interpretation of cache behavior developed by vermiform animals 27,28 . A recent analysis describes relations between deep-marine Zoophycos , sedimentation rate, seasonal primary productivity, and oxygenation 29 . Accordingly, Zoophycos primarily appears in glacial periods with intensive seasonal productivity, reflecting high fluxes and intermediate sedimentation rates from 5 to 20 cm ka −1 .…”

“…Accordingly, Zoophycos primarily appears in glacial periods with intensive seasonal productivity, reflecting high fluxes and intermediate sedimentation rates from 5 to 20 cm ka −1 . Under these conditions, Zoophycos tracemakers collect nutrients at the sediment surface and transport them to deeper layers within the sediment to prevent oxidation 29 .…”

The ichnology of carbonate drifts

“…) and are characterized by a relatively lower degree of bioturbation with identifiable individual traces. Zoophycos is typical of the dark intervals and is considered as an indicator of organic matter deposition (Dorador et al ., ). Chondrites , also significant in these intervals, is an indicator of poor oxygenation below the sediment/water interface in the Danish drifts where they occur with small sizes (Rasmussen & Surlyk, ).…”