Reconstruction of anthropogenic environmental changes from a Cuban coral over the last 160 years
by Marie Harbott, Henry C. Wu, Henning Kuhnert, Anette Meixner, Carlos Jimenez, Patricia GonzalesDiaz and Tim Rixen
Leibniz Zentrum für Marine Tropenforschung | Leibniz Zentrum für Marine Tropenforschung | Faculty of Geosciences & MARUM – Center for Marine Environmental Sciences |Faculty of Geosciences & MARUM – Center for Marine Environmental Sciences | The Cyprus Institute |Centro de Investigaciones Marinas Universidad de la Habana | Leibniz Zentrum für Marine Tropenforschung
Changes in the surface pH and temperature of the ocean, caused by the uptake of anthropogenic CO2, are posing a threat to calcifying marine organisms. The global coverage of studies focusing on ocean pH and carbonate chemistry are sparse and are limiting our understanding of the current situation as well as future developments. Cuba is situated between densely populated landmasses, and offers a unique environment to study multiple aspects of anthropogenic activity as well as their interconnectivity. By using multiple climate and environmental geochemical proxies, a massive Siderastrea siderea coral from Cuba’s northern coast was used to reconstruct changes in SST, ocean pH, and carbonate chemistry since preindustrial times. Preliminary results indicate a decrease in δ18O values indicating warming SST, which is reflected by a decrease in the δ11B signature, a proxy for seawater pH and calcification. Furthermore, an accelerating decrease in δ13C values from the 1950s to 2005 of 0.014‰ suggests the rapid rise in anthropogenic CO2 from fossil fuel combustion that is strongly depleted in 13C reflecting the trend of tropical ocean CO2 uptake. Further investigation and the comparison to trace elements show possible baseline shifts in regional seawater carbonate chemistry that has been affected by anthropogenic activity.
South Pacific convergence zone variability and recent acidification reconstructed from tropical corals
by Sara Todorovic, Henry C. Wu, Delphine Dissard, Henning Kuhnert, Braddock Linsley, AlbertBenthien, Markus Raitzsch, Klaus-Uwe Richter and Jelle Bijma
Leibniz Centre for Tropical MarineResearch, Bremen, Germany | Leibniz Centre for Tropical Marine Research, Bremen, Germany |IRD/UMR LOCEAN (Sorbonne Universités, IRD-CNRS-MNHN), Paris, France | MARUM – Center forMarine Environmental Sciences, University of Bremen, Bremen, Germany | Lamont-Doherty EarthObservatory of Columbia University, Palisades, NY, USA | Alfred Wegener Institute – Helmholz Centre forPolar and Marine Research (AWI), Bremerhaven, Germany | Alfred Wegener Institute – Helmholz Centrefor Polar and Marine Research (AWI), Bremerhaven, Germany | Alfred Wegener Institute – HelmholzCentre for Polar and Marine Research (AWI), Bremerhaven, Germany | Alfred Wegener Institute –Helmholz Centre for Polar and Marine Research (AWI), Bremerhaven, Germany
Massive tropical corals embed extensive records of environmental conditions during their lives, offering a possibility to extend the oceanographic instrumental records available by hundreds of years. Coral based reconstructions allow us to observe oceanographic variability on decadal to centennial scales, including the South Pacific convergence zone (SPCZ) behavior and past El Niño-Southern Oscillation events, which are major drivers of global climate and may exert control on regional CO2 absorption and pH variability. Porites sp. corals from Tonga and Rotuma (Fijian dependency) are being analyzed for multi-proxy (e.g. Sr/Ca, δ18O, δ13C, δ11B, B/Ca) reconstructions of sea surface temperature and salinity (SST, SSS) and seawater carbonate chemistry and pH, on a monthly to annual resolution. Preliminary data of the Rotuma Porites sp. coral shows δ18O signature has been decreasing by 0.004 ‰ per year at the end of the 20th century, suggesting freshening and warming of the surface water. In the same period, we observe a δ13C decrease of 0.017 ‰ per year in-line with the increase in uptake of anthropogenic CO2 which is depleted in this isotope. The results are in agreement with published coral-based reconstructions from the region. When completed, the new records will provide understanding on the effects of modern anthropogenic influence on ocean carbonate system and pH variation over interannual and decadal-interdecadal timescales.
SPCZ zonal and El Niño events impact on surface ocean conditions in the Indonesian Throughflow region
by Henry Wu, Sophie Zweifel, Tim Rixen, Henning Kuhnert and Braddock K. Linsley
ZMT | University of Edinburgh | ZMT | MARUM-Universität Bremen | Lamont-Doherty Earth Observatory of Columbia University
The Indonesian Throughflow (ITF) is an important ocean current that connects the Pacific and Indian Oceans. It is the only low-latitude inter-ocean conduit that annually transports a large amount of water (10–15 sverdrups, where one sverdrup equals 1×106 m3/s) and heat (~0.5 PW, where 1 PW= 1015 W) from the Pacific to 12°S in the Indian Ocean. The ITF follows an intricate pathway through the Indonesian seas on the edge of the western Pacific warm pool (WPWP) and play a key role in modulating Indo-Pacific climate over a range of time scales. The main path for the ITF is the Makassar Strait and the seasonal surface freshening of the Makassar Strait is the factor controlling the ITF. Here we present reconstructions of seasonal sea surface salinity variability by using coral δ18O records from the central Makassar Strait. Coral records reveal persistent seasonal freshening and years with significantly truncated seasonal freshening that correlate exactly with South Pacific Convergence Zone (SPCZ) zonal events >4000 km to the east. These truncated SPCZ zonal events coincide with El Niño/Southern Oscillation warm events halting the normal seasonal freshening in the Strait and thus the ITF. Our coral δ18O time series provides the recurrence interval of these zonal SPCZ events and demonstrate that they have occurred on a semi-regular basis since the mid-1700s. Preliminary coral skeletal trace element-based sea surface temperature reconstructions may provide additional evidence of interannual to interdecadal heat exchange between the Pacific and the Indian Oceans from the ITF.
Thunderstorm self-organization and its effect on tropical coasts
by Jan O. Haerter
ZMT/University of Copenhagen
Tropical thunderstorms are fascinating as they have the ability to cluster, that is, bunch together in larger groups of moist air updrafts, with clusters often spanning hundreds of kilometers. When organized, precipitation intensifies and wind speed can strongly increase, thus posing a threat to communities and ecosystems in terms of mechanical destruction or flash flooding. We study such self-organization both over continents and the sea, and contrast the emergent dynamics. In a process we term “diurnal self-aggregation” clusters akin to mesoscale convective systems (MCS) form within few days in numerical simulations over continental surfaces. Over the ocean, self-organization is much slower, but reaches profoundly segregated states after several weeks. Both mechanisms may be relevant to the initial formation of tropical cyclones, which are known to intensify over warm waters, when rotational acceleration is provided away from the equator.