Regional and global changes during Heinrich Event 1 affecting macrobenthic habitat: Ichnological evidence of sea-bottom conditions at the Galicia Interior Basin

Abstract

Abstract Heinrich events (HEs) are climatic changes, occurring during the Pleistocene, related to massive discharge of freshwater from the Laurentide Ice Sheet, through the Hudson Strait, recognized in the sedimentary record through distinctive layers of ice-rafted detritus (IRD), the so-called Heinrich layers (HLs). Environmental changes during HEs influence significantly in marine biota (i.e. modifications in composition and abundance of assemblages), with ecological and evolutionary consequences. This point has been only partially addressed in particular groups (e.g. microorganisms), whereas interactions with other groups remain understudied. Here, we analyse ichnological features of the Heinrich layer 1, associated to Heinrich Event 1 (HE1), from several gravity cores at the Galicia Interior Basin (NW Iberian Peninsula) to test the influence of this HE1 on environmental parameters, such as bottom and pore-water oxygenation, as well as benthic food availability, conforming the macrobenthic habitat. Freshwater input during the first phase of the HE1 caused unfavorable conditions (probably highly dysoxic to anoxic) for tracemakers, as revealed by the absence of both discrete traces and a well-developed mottled background. However, the tracemaker community was reestablished shortly after deposition of the ice-rafted detritus layer (Heinrich layer) of HE1, as reflected by the significant increase in diversity and abundance of traces (Planolites, Thalassinoides, Thalassinoides-like, Chondrites, and Zoophycos), revealing a major shift to oxic bottom and pore waters and likely benthic food. This global/general pattern, though, is affected by the regional setting and by the associated predominant sedimentation processes, leading to a variable incidence of paleoenvironmental changes associated with HE1. The ecological impact on macrobenthic biota, in term of changes in diversity and abundance of tracemakers, by HE1 soon attenuates, resulting in a negligible evolutionary impact.