Transport Bias by Ocean Currents in Sedimentary Microplankton Assemblages: Implications for Paleoceanographic Reconstructions

Abstract

Microfossils from plankton are used for paleoceanographic reconstructions. An often-made assumption in quantitative microplankton-based paleoceanographic reconstructions is that sedimentary assemblages represent conditions of the directly overlying surface water. However, any immobile particle sinking down the water column is subjected to transport by three-dimensional currents, which results in a lateral relocation along transport. We model dinoflagellate cyst (dinocyst) transport in a high-resolution (0.1 • horizontally) global model of the present-day ocean and compare ocean conditions in the simulated origin of sedimentary particles to that in the directly overlying water. We find that the assumption that sedimentary particles represent the overlying surface waters is in most regions not valid. The bias induced by dinocyst transport depends on ocean current strength and direction, aggregation of particles which could increase the sinking speed, and the sediment sample depth. By using realistic sinking speeds of dinocysts and aggregates, extreme biases up to approximately ±16 • C warmer or ±4 PSU saltier are found, while other regions show lower bias from particle transport. Our model results provide a way to mechanistically and statistically explain the unexpected occurrences of some dinocyst species outside of their "normal" occurrence region, such as the northerly occurrence of the allegedly sea-ice-affiliated dinocyst Selenopemphix antarctica. Exclusion of such outlier occurrences will yield better constrained ecological affinites for dinocyst species, which has implications for microfossil-based quantitative and qualitative proxies for paleoceanographic conditions. We recommend paleoceanographers to a priori evaluate the (paleo)water depth, oceanographic setting, current strength, and particle aggregation probability for their sedimentary microplankton assemblages.

Resolution dependency of sinking Lagrangian particles in ocean general circulation models

“…The lateral transport of sinking particles can be estimated using Ocean General Circulation Models (OGCMs) and Lagrangian tracking techniques [9]. The Lagrangian techniques are used to model the sinking particle trajectories in the modern ocean [10][11][12][13][14][15], specifically for sinking microplankton [16,17] and microplastic [18].…”

“…The tool can also be used to determine how the microplankton in the bottom sediments at any location of choice relates to the environment at these origin locations (e.g. temperature, salinity, primary productivity) in the present-day ocean (see also [17]).…”

Dinocyst and acritarch biostratigraphy of the Late Pliocene to Early Pleistocene at Integrated Ocean Drilling Program Site U1307 in the Labrador Sea

“…But the occurrence of Melitasphaeridium choanophorum in the western North Atlantic in DSDP Hole 603C through the Pliocene and Early Pleistocene (Martin J. Head, unpublished data in De Schepper et al, 2017), on the Scotian Shelf and Grand Banks in the Pliocene and the Late Gelasian (Williams and Bujak, 1977), and even in recent sediments of the Gulf of Mexico (Limoges et al, 2013(Limoges et al, , 2014Price et al, 2017) indicates a more extended range than previously thought and affinities for subtropical conditions. Its diachronous disappearance from the Pliocene North Atlantic and persistence in the Gulf of Mexico may be related to cooling and the intensification of glaciation during the Quaternary.…”

Evaluation of isotopes and elements in planktonic foraminifera from the Mediterranean Sea as recorders of seawater oxygen isotopes and salinity

“…This may add to the uncertainty in the variable to cross-correlate against or even introduce a bias in the resulting calibration. Recently this has been shown for dinoflagellate cysts (Nooteboom et al, 2019) and planktonic foraminifera, collected from sediment (van Sebille et al, 2015) and also from sediment traps (Steinhardt et al, 2014), but can also be applied to specimens collected living from the sea surface.…”