Figen Mekik

Oceanic conditions in the eastern equatorial Pacific during the onset of ENSO in the Holocene

Abstract Records from South America show that modern ENSO (El Nino-Southern Oscillation) did not exist 7000 cal yr B.P. and has developed progressively since then. There has been little information available on oceanic conditions in the eastern equatorial Pacific (EEP) to constrain explanations for ENSO onset. We report quantitative observations on thermocline and mixed-layer conditions in the EEP during ENSO start up. We found important changes in both the thermocline and the mixed layer, indicating increased upwelling of cooler waters since 7000 cal yr B.P. This resulted from change in the source and/or properties of waters supplying the Equatorial Undercurrent, which feeds upwelling along the equator and the Peru margin. Modeling shows that ENSO is sensitive to subsurface conditions in the eastern equatorial Pacific and that the changes in the thermocline we observed were driven by extratropical processes, giving these a role in conditioning the development of ENSO. This is in contrast to models that call for control of equatorial Pacific oceanography by tropical processes only. These infer stronger upwelling and cooler surface waters for the EEP during the mid-Holocene, which is not supported by our results.

Effects of surface ocean conditions on deep‐sea calcite dissolution proxies in the tropical Pacific

Finding the ideal deep-sea CaCO3 dissolution proxy is essential for quantifying the role of the marine carbonate system in regulating atmospheric pCO2 over millennia. We explore the potential of using the Globorotalia menardii fragmentation index (MFI) and size-normalized foraminifer shell weight (SNSW) as complementary indicators of deep-sea CaCO3 dissolution. MFI has strong correlations with bottom water [CO32−], modeled estimates of percent CaCO3 dissolved, and Mg/Ca in Pulleniatina obliquiloculata in core top samples along a depth transect on the Ontong Java Plateau (OJP) where surface ocean temperature variation is minimal. SNSW of P. obliquiloculata and Neogloboquadrina dutertrei have weak correlations with MFI-based percent dissolved, Mg/Ca in P. obliquiloculata shells and bottom water [CO32−] on the OJP. In core top samples from the eastern equatorial Pacific (EEP), SNSW of P. obliquiloculata has moderate to strong correlations with both MFI-based percent CaCO3 dissolved estimates and surface ocean environmental parameters. SNSW of N. dutertrei shells shows a latitudinal distribution in the EEP and a moderately strong correlation with MFI-based percent dissolved estimates when samples from the equatorial part of the region are excluded. Our results suggest that there may potentially be multiple genotypes of N. dutertrei in the EEP which may be reflected in their shell weight. MFI-based percent CaCO3 dissolved estimates have no quantifiable relationship with any surface ocean environmental parameter in the EEP. Thus MFI acts as a reliable quantitative CaCO3 dissolution proxy insensitive to environmental biases within calcification waters of foraminifers.

Deep‐sea sediments

Often unnoticed by the casual observer, every second of every day the oceans record the passing of time and the interaction of ocean, land, and atmosphere, grain after grain, precipitate after precipitate. Deep marine sediments serve as archives recording the history of ocean basins and lend insights into the rates and magnitudes of climatic and environmental change. As such, a collection of articles on recent cutting-edge research summarizing various marine environments and processes is important and necessary for any Earth scientist. Such a compilation is particularly important for undergraduate and graduate audiences as well as educators charged with teaching them.