Coral geochemical response to uplift in the aftermath of the 2005 Nias–Simeulue earthquake

On 28 March 2005, the Indonesian islands of Nias and Simeulue experienced a powerful Mw 8.6 earthquake and coseismic uplift and subsidence. In areas of coastal uplift (up to ~ 2.8 m), fringing reef coral communities were killed by exposure, while deeper corals that survived were subjected to habitats with altered runoff, sediment and nutrient regimes. Here we present time-series (2000–2009) of Mn/Ca, Y/Ca and Ba/Ca variability in massive Porites corals from Nias to assess the environmental impact of a wide range of vertical displacement (+ 2.5 m to − 0.4 m). High-resolution LA-ICP-MS measurements show that skeletal Mn/Ca increased at uplifted sites, regardless of reef type, indicating a post-earthquake increase in suspended sediment delivery. Transient and/or long-term increases in skeletal Y/Ca at all uplift sites support the idea of increased sediment delivery. Coral Mn/Ca and Ba/Ca in lagoonal environments highlight the additional influences of reef bathymetry, wind-driven sediment resuspension, and phytoplankton blooms on coral geochemistry. Together, the results show that the Nias reefs adapted to fundamentally altered hydrographic conditions. We show how centuries of repeated subsidence and uplift during great-earthquake cycles along the Sunda megathrust may have shaped the modern-day predominance of massive scleractinian corals on the West Sumatran reefs

Sea ice dynamics across the Mid-Pleistocene transition in the Bering Sea.

Sea ice and associated feedback mechanisms play an important role for both long- and short-term climate change. Our ability to predict future sea ice extent, however, hinges on a greater understanding of past sea ice dynamics. Here we investigate sea ice changes in the eastern Bering Sea prior to, across, and after the Mid-Pleistocene transition (MPT). The sea ice record, based on the Arctic sea ice biomarker IP25 and related open water proxies from the International Ocean Discovery Program Site U1343, shows a substantial increase in sea ice extent across the MPT. The occurrence of late-glacial/deglacial sea ice maxima are consistent with sea ice/land ice hysteresis and land-glacier retreat via the temperature-precipitation feedback. We also identify interactions of sea ice with phytoplankton growth and ocean circulation patterns, which have important implications for glacial North Pacific Intermediate Water formation and potentially North Pacific abyssal carbon storage

Patterns and mechanisms of early Pliocene warmth

About five to four million years ago, in the early Pliocene epoch, Earth had a warm, temperate climate. The gradual cooling that followed led to the establishment of modern temperature patterns, possibly in response to a decrease in atmospheric CO2 concentration, of the order of 100 parts per million, towards preindustrial values. Here we synthesize the available geochemical proxy records of sea surface temperature and show that, compared with that of today, the early Pliocene climate had substantially lower meridional and zonal temperature gradients but similar maximum ocean temperatures. Using an Earth system model, we show that none of the mechanisms currently proposed to explain Pliocene warmth can simultaneously reproduce all three crucial features. We suggest that a combination of several dynamical feedbacks underestimated in the models at present, such as those related to ocean mixing and cloud albedo, may have been responsible for these climate conditions

The Great American Biotic Interchange: Dispersals, Tectonics, Climate, Sea Level and Holding Pens

The biotic and geologic dynamics of the Great American Biotic Interchange are reviewed and revised. Information on the Marine Isotope Stage chronology, sea level changes as well as Pliocene and Pleistocene vegetation changes in Central and northern South America add to a discussion of the role of climate in facilitating trans-isthmian exchanges. Trans-isthmian land mammal exchanges during the Pleistocene glacial intervals appear to have been promoted by the development of diverse non-tropical ecologies

Navigating Miocene ocean temperatures for insights into the future

A new temperature data portal will aid scientists in tracking and accessing paleoclimate data from the Miocene, a past warm climate interval and future climate analogue

North Atlantic climate evolution through the Plio-Pleistocene climate transitions

During the Plio-Pleistocene, the Earth witnessed the growth of large northern hemisphere ice sheets and profound changes in both North Atlantic and global climate. Here, we present a ~ 3.2 Myr long, orbitally-resolved alkenone sea surface temperature (SST) record from Deep Sea Drilling Project (DSDP) Site 607 (41°N, 33°W, water depth 3427 m) in the North Atlantic Ocean. We employ a multi-proxy approach comparing these new observations with existing bottom water temperature (BWT) and stable isotope time series from the same site and SST time series from other sites, shedding new light on Plio-Pleistocene climate change. North Atlantic temperature records show a long-term cooling with two major steps occurring during the late Pliocene (3.1 to 2.4 Ma) and the mid-Pleistocene (1.5 to 0.8 Ma), closely timed with intervals of major change in northern hemisphere ice sheets. Existing evidence suggests that the late Pliocene cooling may have been caused by a thresholded response to secular changes in atmospheric carbon dioxide (CO2). While an explanation for the mid-Pleistocene cooling may involve glacial–interglacial changes in atmospheric CO2, it seems to also require a change in the behavior of the ice sheets themselves. North Atlantic climate responses were closely phased with benthic oxygen isotope (δ18O) changes during the “41 kyr world,” indicating a strong common northern hemisphere high latitude imprint on North Atlantic climate signals. After the mid-Pleistocene transition (MPT), North Atlantic SST records and the Site 607 benthic carbon isotope (δ13C) record are more closely phased with δ18O, whereas BWT significantly leads δ18O in the 100 kyr band, suggesting a shift from a northern to a southern hemisphere influence on North Atlantic BWT. We propose that the expansion of the West Antarctic ice sheet (WAIS) across the MPT increased the production and export of Antarctic Bottom Water from the Southern Ocean and subsequently controlled its incursion into the North Atlantic, especially during glacial intervals. It follows that the early 100 kyr response of BWT implies an early response of the WAIS relative to the northern hemisphere deglaciation. Thus, in the “100 kyr world,” both northern hemisphere and southern hemisphere processes affect climate conditions in the North Atlantic Ocean

Breathing more deeply: Deep ocean carbon storage during the mid Pleistocene Transition

The ~100 k.y. cyclicity of the late Pleistocene ice ages started during the mid-Pleistocene transition (MPT), as ice sheets became larger and persisted for longer. The climate system feedbacks responsible for introducing this nonlinear ice sheet response to orbital variations in insolation remain uncertain. Here we present benthic foraminiferal stable isotope (δ18O, δ13C) and trace metal records (Cd/Ca, B/Ca, U/Ca) from Deep Sea Drilling Project Site 607 in the North Atlantic. During the onset of the MPT, glacial-interglacial changes in δ13C values are associated with changes in nutrient content and carbonate saturation state, consistent with a change in water mass at our site from a nutrient-poor northern source during interglacial intervals to a nutrient-rich, corrosive southern source during glacial intervals. The respired carbon content of glacial Atlantic deep water increased across the MPT. Increased dominance of corrosive bottom waters during glacial intervals would have raised mean ocean alkalinity and lowered atmospheric pCO2. The amplitude of glacial-interglacial changes in δ13C increased across the MPT, but this was not mirrored by changes in nutrient content. We interpret this in terms of air-sea CO2 exchange effects, which changed the δ13C signature of dissolved inorganic carbon in the deep water mass source regions. Increased sea ice cover or ocean stratification during glacial times may have reduced CO2 outgassing in the Southern Ocean, providing an additional mechanism for reducing glacial atmospheric pCO2. Conversely, following the establishment of the ~100 k.y. glacial cycles, δ13C of interglacial northern-sourced waters increased, perhaps reflecting reduced invasion of CO2 into the North Atlantic following the MPT