Description: Glacial meltwater discharge from Antarctica is a key influence on the marine environment, impacting ocean circulation, sea level, and productivity of the pelagic and benthic ecosystems. The responses elicited depend strongly on the characteristics of the meltwater releases, including timing, spatial structure and geochemical composition. Here we use isotopic tracers to reveal the time-varying pattern of meltwater during a discharge event from the Fourcade Glacier into Potter Cove, northern Antarctic Peninsula. The discharge is strongly dependent on local air temperature, and accumulates into an extremely thin, buoyant layer at the surface. This layer showed evidence of elevated turbidity, and responded rapidly to changes in atmospherically-driven circulation to generate a strongly pulsed outflow from the cove to the broader ocean. These characteristics contrast with those further south along the Peninsula, where strong glacial frontal ablation is driven oceanographically by intrusions of warm deep waters from offshore. The Fourcade Glacier switched very recently to being land-terminating; if retreat rates elsewhere along the Peninsula remain high and glacier termini progress strongly landward, the structure and impact of the freshwater discharges are likely to increasingly resemble the patterns elucidated here.

Description: Glacial meltwater discharge from Antarctica is a key influence on the marine environment, impacting ocean circulation, sea level, and productivity of the pelagic and benthic ecosystems. The responses elicited depend strongly on the characteristics of the meltwater releases, including timing, spatial structure and geochemical composition. Here we use isotopic tracers to reveal the time-varying pattern of meltwater during a discharge event from the Fourcade Glacier into Potter Cove, northern Antarctic Peninsula. The discharge is strongly dependent on local air temperature, and accumulates into an extremely thin, buoyant layer at the surface. This layer showed evidence of elevated turbidity, and responded rapidly to changes in atmospherically-driven circulation to generate a strongly pulsed outflow from the cove to the broader ocean. These characteristics contrast with those further south along the Peninsula, where strong glacial frontal ablation is driven oceanographically by intrusions of warm deep waters from offshore. The Fourcade Glacier switched very recently to being land-terminating; if retreat rates elsewhere along the Peninsula remain high and glacier termini progress strongly landward, the structure and impact of the freshwater discharges are likely to increasingly resemble the patterns elucidated here.

Description: Temperature reconstructions indicate that the Pliocene was approximately 3°C warmer globally than today, and several recent reconstructions of Pliocene atmospheric CO2 indicate that it was above pre-industrial levels and similar to those likely to be seen this century. However, many of these reconstructions have been of relatively low temporal resolution, meaning that these records may have failed to capture variations associated with the 41 kyr glacial–interglacial cycles thought to have operated in the Pliocene. Here we present a new, high temporal resolution alkenone carbon isotope-based record of pCO2 spanning 3.3–2.8 Ma from Ocean Drilling Program Site 999. Our record is of high enough resolution (approx. 19 kyr) to resolve glacial–interglacial changes beyond the intrinsic uncertainty of the proxy method. The record suggests that Pliocene CO2 levels were relatively stable, exhibiting variation less than 55 ppm. We perform sensitivity studies to investigate the possible effect of changing sea surface temperature (SST), which highlights the importance of accurate and precise SST reconstructions for alkenone palaeobarometry, but demonstrate that these uncertainties do not affect our conclusions of relatively stable pCO2 levels during this interval.

Description: To test the pore density in benthic foraminifera as a potential proxy for bottom-water oxygenation, pore density analyses were carried out on tests of living (rose Bengal-stained) specimens of the deep-infaunal and anoxia-tolerant foraminiferal species Globobulimina turgida. Three stations within and two stations below the oxygen minimum zone (OMZ) off Namibia were investigated and compared to in situ-measured bottom-water oxygen content (BW-O2). Pore density was first conventionally assessed by rather time-consuming manual pore counting on SEM photographs and measurement of the analyzed test areas. To significantly shorten the measurement time we tested and evaluated an automation of the pore density measurement using the image analysis software package analySIS (version 5.0, Olympus Soft Imaging Solutions). Pore density data from automated analyses are compared to manually acquired data from G. turgida. Our study shows almost identical results for both manually and automatically acquired data. Consequently, we assume that the new technique provides an alternative and more rapid method to analyze the pore density of foraminifera. For both methods, our results show a distinct negative linear correlation (automatically analyzed pore density: τ = −0.50, p 〈 0.001; manually analyzed pore density: τ = −0.49, p 〈 0.001) between pore density and BW-O2, suggesting that G. turgida increases its pore density in response to decreasing oxygen. Thus, we suggest that, similar to other recently described low-oxygen-tolerant benthic foraminiferal species, G. turgida may improve its O2 uptake by increasing pore density to survive in low-oxic environments. This morphological adaption might be useful for future studies to establish an independent proxy for BW-O2. In addition, pore density has been compared to in situ-measured bottom-water nitrate concentration (BW-NO3−). Our investigation of the pore density-to-BW-NO3− relationship for G. turgida suggests that nitrate seems to be a minor factor influencing pore density in this species compared to BW-O2. Add to CiteULike