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

Although bioturbation is commonly recognized in contourites, only a few studies have analyzed the ichnological content of these deposits in detail. These studies have mainly focused on meso-scale bigradational sequence (a coarsening upward followed by a fining-upward sequence resulting from variations in current velocity). Here we present data from gravitational cores collected along the NW Iberian Margin showing systematic variation in ichnological content across proximal to distal depocenters within a large-scale elongated contourite drift. Data demonstrate that tracemakers’ behavior varies depending on the distance relative to the bottom current core. Trace fossils are already known to be a useful tool for studying of contouritic deposits and are even used as criterion for differentiating associated facies (e.g., turbidites, debrites), though not without controversy. We propose a mechanism by which the distance to the bottom current core exerts tangible influence on specific macro-benthic tracemaker communities in contourite deposits. This parameter itself reflects other bottom current features, such as hydrodynamic energy, grain size, nutrient transport, etc. Ichnological analysis can thus resolve cryptic features of contourite drift depositional settings.European Commission | Ref. H2020, n. 792314Universidad de Granada | Ref. UCE-2016- 05Xunta de Galicia | Ref. ED481B 2016/029-0Junta de Andalucía | Ref. CGL2015-66835-

Coccolithophore productivity and surface water dynamics in the Alboran Sea during the last 25 kyr

Coccolithophore productivity and surface water dynamics for the last 25 kyr in the Alboran Sea (Western Mediterranean) are described in a study of high-resolution sedimentary records from two cores, HER-GC-T1 and CEUTA10PC08, whose locations are currently characterized by different hydrographic conditions. Fossil coccolithophore assemblages and oxygen isotopes and alkenone- and planktonic foraminifera-derived sea surface temperature (SST) records allowed a reconstruction of the properties of the inflowing Atlantic Water (AW), which have proved to be a primary control of the variations in productivity in the neighborhood of the Strait of Gibraltar. Other local factors, such as fluvial discharge, wind-induced and eddy-induced upwelling, are proposed to have influenced marine productivity in more distant areas. The entrance of cold and less saline AW during the stadials associated with Heinrich events 2 and 1 prevented primary productivity, which increased along the Last Glacial Maximum, probably due to a greater fluvial discharge. During Terminations 1a and 1b, the upper water column was affected by stratification, although wind-induced upwelling occurred locally. The Bølling–Allerød was characterized by a gradual increase in productivity and the development of the organic-rich layer. Two phases of the Younger Dryas are recognized: a first phase, which was colder, followed by a second phase, which was warmer and wetter. Differences in productivity between both locations during these two phases can be attributed to fluvial discharge and the changing properties of the AW. Local hydrography, such as the dynamics of the western anticyclonic gyre, gained greater importance in determining productivity and its variations during the Holocene, which was the most productive period.Ministerio de Ciencia e Innovación | Ref. CTM2008-06399-C04Agencia Estatal de Investigación | Ref. CTM2012-39599-03-01Ministerio de Educación | Ref. AP2010-255