Paleoclimate reconstructions from sediment core MD01-2378

On the basis of the radiocarbon (14C) plateau-tuning method a new age model for Timor Sea Core MD01-2378 was established. It revealed a precise centennial-scale phasing of climate events in the ocean, cryo-, and atmosphere during the last deglacial and provides important new insights into causal linkages controlling events of global climate change. At Site MD01-2378 reservoir ages of surface waters dropped from 1600 yr prior to 20 cal ka to 250-500 yr after 18.8 cal ka. This evidence was crucial for generating a high-resolution age model for deglacial events in the Indo-Pacific Warm Pool. Sea-surface temperatures (SST) started to change near 18.8 cal ka, that is ~500 yr after the start of, presumably northern hemispheric, deglacial melt and sea level rise as shown by the benthic foraminiferal oxygen isotope ratio (d18O). However, the SST rise occurred 500-1000 yr prior to the onset of deglacial Antarctic warming and the first major rise in atmospheric carbon dioxide at about 18 ka. The increase in SST may partly reflect reduced seasonal upwelling of cold subsurface waters along the eastern margin of the Indian Ocean, which is reflected by a doubling of the thermal gradient between the sea surface and the thermocline, a halving of chlorin productivity from 19 to 18.5 cal ka, and in particular, by the strong decrease in surface water reservoir ages. Two significant increases in deglacial Timor Sea surface salinities from 19-18.5 and 15.5-14.5 cal ka, may partly reflect the deglacial increase in the distance of local river mouths, partly an inter-hemispheric millennial-scale see-saw in tropical monsoon intensity, possibly linked to a deglacial increase in the dominance of Pacific El Niño regimes over Heinrich stadial 1.

Chemistry of Globigerinoides ruber shells from ODP Site 160-963

Here we present a high-resolution faunal, floral and geochemical (stable isotopes and trace elements) record from the sediments of Ocean Drilling Program Site 963 (central Mediterranean basin), which shows centennial/millennial-scale resemblance to the high-northern latitude rapid temperature fluctuations documented in the Greenland ice cores between 20 and 70 kyr BP. Oxygen and carbon isotopes, planktic foraminifera and calcareous nannofossil distributions suggest that Dansgaard-Oeschger (D/O) and Heinrich events (HE) are distinctly expressed in the Mediterranean climate record. Moreover, recurrent though subdued oscillations not previously identified in the Lateglacial Mediterranean sediments document a significant centennial-scale climate variability in the basin that is greater than previously thought. Alternations between climate regimes dominated by polar outbreaks during D/O stadials and warm D/O interstadials, with associated intensification of continental runoff, are well expressed in the ODP Site 963. These place the Mediterranean basin as an often overlooked recorder of the interplay between large- and regional- scale climate controls at intermediate latitudes, and of the possible interactions between different components of the climate system. Significant changes in Ba/Ca values measured in Globigerinoides ruber shells from a number of D/O stadials and interstadials suggest enhanced freshwater input from the north-eastern Mediterranean borderland during the D/O interstadials. However, the short duration of 3D stratification events never led to complete oxygen consumption along the water column, but clear effects of sluggish 3D circulation in the basin are testified to by negative excursions in d13C measured in selected species of planktic and benthic foraminifera. HEs are constantly associated with lightening in the d18O record of planktic foraminifera, possibly because of the impact of iceberg melting in the Iberian Margin on Mediterranean thermohaline circulation. Interestingly, in two cases in particular, HE2 and HE5, fresher water inputs also affected deeper horizons of intermediate waters, suggesting a basin-wide impact.

Gas emissions and ROV survey tracks of the Regab pockmark (Northern Congo Fan)

Pockmarks are seafloor depressions commonly associated with fluid escape from the seabed and are believed to contribute noticeably to the transfer of methane into the ocean and ultimately into the atmosphere. They occur in many different areas and geological contexts, and vary greatly in size and shape. Nevertheless, the mechanisms of pockmark growth are still largely unclear. Still, seabed methane emissions contribute to the global carbon budget, and understanding such processes is critical to constrain future quantifications of seabed methane release at local and global scales. The giant Regab pockmark (9°42.6' E, 5°47.8' S), located at 3160 m water depth near the Congo deep-sea channel (offshore southwestern Africa), was investigated with state-of-the-art mapping devices mounted on IFREMER's (French Research Institute for Exploitation of the Sea) remotely operated vehicle (ROV) Victor 6000. ROV-borne micro-bathymetry and backscatter data of the entire structure, a high-resolution photo-mosaic covering 105,000 m2 of the most active area, sidescan mapping of gas emissions, and maps of faunal distribution as well as of carbonate crust occurrence are combined to provide an unprecedented detailed view of a giant pockmark. All data sets suggest that the pockmark is composed of two very distinctive zones in terms of seepage intensity. We postulate that these zones are the surface expression of two fluid flow regimes in the subsurface: focused flow through a fractured medium and diffuse flow through a porous medium. We conclude that the growth of giant pockmarks is controlled by self-sealing processes and lateral spreading of rising fluids. In particular, partial redirection of fluids through fractures in the sediments can drive the pockmark growth in preferential directions.

Source data for Plos ONE publication Redefining thermal regimes to design reserves for coral reefs in the face of climate change

Reef managers cannot fight global warming through mitigation at local scale, but they can use information on thermal patterns to plan for reserve networks that maximize the probability of persistence of their reef system. Here we assess previous methods for the design of reserves for climate change and present a new approach to prioritize areas for conservation that leverages the most desirable properties of previous approaches. The new method moves the science of reserve design for climate change a step forwards by: (1) recognizing the role of seasonal acclimation in increasing the limits of environmental tolerance of corals and ameliorating the bleaching response; (2) including information from several bleaching events, which frequency is likely to increase in the future; (3) assessing relevant variability at country scales, where most management plans are carried out. We demonstrate the method in Honduras, where a reassessment of the marine spatial plan is in progress.