Evidence for influx of Atlantic water masses to the Labrador Sea during the Last Glacial Maximum.

The Last Glacial Maximum (LGM, 23-19,000 year BP) designates a period of extensive glacial extent and very cold conditions on the Northern Hemisphere. The strength of ocean circulation during this period has been highly debated. Based on investigations of two marine sediment cores from the Davis Strait (1033 m water depth) and the northern Labrador Sea (2381 m), we demonstrate a significant influx of Atlantic-sourced water at both subsurface and intermediate depths during the LGM. Although surface-water conditions were cold and sea-ice loaded, the lower strata of the (proto) West Greenland Current carried a significant Atlantic (Irminger Sea-derived) Water signal, while at the deeper site the sea floor was swept by a water mass comparable with present Northeast Atlantic Deep Water. The persistent influx of these Atlantic-sourced waters entrained by boundary currents off SW Greenland demonstrates an active Atlantic Meridional Overturning Circulation during the LGM. Immediately after the LGM, deglaciation was characterized by a prominent deep-water ventilation event and potentially Labrador Sea Water formation, presumably related to brine formation and/or hyperpycnal meltwater flows. This was followed by a major re-arrangement of deep-water masses most likely linked to increased overflow at the Greenland-Scotland Ridge after ca 15 kyr BP.

Impact of drill cutting releases on benthic foraminifera at three exploration wells drilled between 1992 and 2012 in the SW Barents Sea, Norway.

The aim of this study is to identify the environmental impact of drill cuttings (DC) released around three wells drilled in 1992, 2000 and 2012 in the SW Barents Sea. Foraminiferal assemblages are studied in cores taken along transects <250 m from wells. Well E-1992 shows no impact of DC on foraminifera indicating that low amounts of released DC limit environmental impact. Impact at wells G-2000 and S-2012, is confined to <30 m, and attributable to smothering of fauna, resulting in low foraminiferal density. We therefore argue that previous monitoring studies, mainly focusing on samples collected >250 m from wellheads, might not capture the full impact of DC. In well G-2000, a recovery layer indicates partial recovery 15 years after DC releases. In well S-2012, no recovery is observed, 3 years after release. Released DC did not result in faunal composition changes.

Spreading of drill cuttings and sediment recovery of three exploration wells of different ages, SW Barents Sea, Norway.

Five stations (≤250 m from the well heads) from three exploration wells of different ages from the SW Barents Sea were studied to investigate the spreading of drill cuttings and sediment quality. Two of the wells were drilled before the restriction of use of oil-based drilling fluids (1993). Elevated concentrations of Ba were found in sediments near all the wells with the highest concentrations at ≤60 m from the well head. The thickness of drill cutting layers was between >20 cm (well head) and 2 cm (250 m from the well head). The sediment quality varied from very bad (oldest well) to background (normal) (newer wells). Regulations led to better sediment quality. Metal concentrations from the oldest well suggested that the top 4 cm of the core represents sediment recovery. However, Ba concentrations of the top sediment layer at all the stations of the three wells indicate no physical recovery.

Identifying past petroleum exploration related drill cutting releases and influences on the marine environment and benthic foraminiferal communities, Goliat Field, SW Barents Sea, Norway.

The present multiproxy investigation of marine sediment cores aims at: 1) Identifying dispersion of petroleum exploration related drill cutting releases within the Goliat Field, Barents Sea in 2006/07 and 2) Assessing past and present influence of drill cuttings on the marine environment. The cores were recovered 5, 30, 60, 125 and 250m from the drill site in the eastward downstream direction. Downstream dispersion of drill cuttings is evaluated by examining sediment grain size distribution and barium (Ba), heavy metal, total organic carbon and sulphur concentrations. Dispersion of drill cuttings was limited to <125m east from the drill site. Influence of drill cutting releases on the marine environment is assessed via microfaunal analysis of primarily calcareous benthic foraminifera. The findings suggest contemporaneous physical smothering at ≤30m from the drill site, with a natural fauna reestablishing after drilling cessation indicating no long-term effect of drill cutting releases.

Environmental baselines and reconstruction of Atlantic Water inflow in Bjørnøyrenna, SW Barents Sea, since 1800 CE.

Metal concentrations, sediment properties and benthic foraminiferal assemblages were investigated in sediment cores in the SW Barents Sea, to reconstruct environmental baselines and natural variability of Atlantic Water inflow since 1800 CE. Metal concentrations correspond to no effect levels and do not influence the foraminifera. Increased Hg and Pb was linked to inflow of Atlantic Water. The data set is considered to reflect the pre-impacted environmental baseline and range in natural variability of the study area. The foraminiferal assemblages in the SW part of the study area showed warming and presence of Atlantic Water towards 1900 CE. The NE part of the region indicate presence of cold Artic Water influenced conditions. Between 1900 and 1980 CE, the SW region indicates reduced inflow of Atlantic Water. From 1980 CE towards the present the assemblages of the entire study area show warming of Atlantic Water and northward retreat of the Arctic Front.