Rapid glaciation and a two-step sea level plunge into the Last Glacial Maximum.

The approximately 10,000-year-long Last Glacial Maximum, before the termination of the last ice age, was the coldest period in Earth's recent climate history1. Relative to the Holocene epoch, atmospheric carbon dioxide was about 100 parts per million lower and tropical sea surface temperatures were about 3 to 5 degrees Celsius lower2,3. The Last Glacial Maximum began when global mean sea level (GMSL) abruptly dropped by about 40 metres around 31,000 years ago4 and was followed by about 10,000 years of rapid deglaciation into the Holocene1. The masses of the melting polar ice sheets and the change in ocean volume, and hence in GMSL, are primary constraints for climate models constructed to describe the transition between the Last Glacial Maximum and the Holocene, and future changes; but the rate, timing and magnitude of this transition remain uncertain. Here we show that sea level at the shelf edge of the Great Barrier Reef dropped by around 20 metres between 21,900 and 20,500 years ago, to -118 metres relative to the modern level. Our findings are based on recovered and radiometrically dated fossil corals and coralline algae assemblages, and represent relative sea level at the Great Barrier Reef, rather than GMSL. Subsequently, relative sea level rose at a rate of about 3.5 millimetres per year for around 4,000 years. The rise is consistent with the warming previously observed at 19,000 years ago1,5, but we now show that it occurred just after the 20-metre drop in relative sea level and the related increase in global ice volumes. The detailed structure of our record is robust because the Great Barrier Reef is remote from former ice sheets and tectonic activity. Relative sea level can be influenced by Earth's response to regional changes in ice and water loadings and may differ greatly from GMSL. Consequently, we used glacio-isostatic models to derive GMSL, and find that the Last Glacial Maximum culminated 20,500 years ago in a GMSL low of about -125 to -130 metres.

Millennial scale maximum intensities of typhoon and storm wave in the northwestern Pacific Ocean inferred from storm deposited reef boulders.

Typhoons and associated storm waves in the northwestern Pacific Ocean commonly cause coastal disasters. The possibility remains that an even stronger typhoon than the strongest one observed to date might have occurred before. The development of a method to estimate a maximum intensity of past typhoons over thousands of years is important for paleoclimatology, paleoceanography and disaster prevention. Numerous storm wave boulders exist on reefs in the Ryukyu Islands, Japan, which have been deposited to their present position by the cumulative effects of the past storm waves. These boulders can be used as proxies for the hydrodynamic conditions of the largest waves from past events. Here, we present numerical computations for storm waves and boulder transport with the boulder distribution as a constraint factor to estimate the maximum intensities of storm waves and their causative typhoon events over the past 3500 years. Though the intensities of the maximum estimated waves and associated typhoon events were slightly stronger than those recorded over the past ~70 years in the Ryukyu Islands, our results suggest that no abnormally intense typhoon has struck the Ryukyu Islands in the past 3500 years. The potential impact from tsunamis remains uncertain; however, our results are meteorologically reasonable.

Coral skeletal tin and copper concentrations at Pohnpei, Micronesia: possible index for marine pollution by toxic anti-biofouling paints.

We present 40 year-long skeletal chronologies of tin (Sn) and copper (Cu) from an annually-banded coral (Porites sp.) collected from Pohnpei Island, Micronesia (western equatorial Pacific). Both the elements are present in antifouling marine paints and are released inadvertently into ambient seawater. Especially, Sn has often been used in the form of tributyltin (TBT). Based on a stepwise pretreatment examination, Sn and Cu both inside and outside the aragonite lattice of the coral skeleton show a potential for providing marine pollution indicators. High values of extra-skeletal Cu/Ca and Sn/Ca atomic ratios were found between late 1960s and late 1980s during a period of active use of TBT-based antifouling paints worldwide. However, a significant decrease in both the ratios in the beginning of 1990s can be attributed to regulation of the use of TBT on cargo ships by countries such as the USA, Japan and Australia.

Influence of land development on Holocene Porites coral calcification at Nagura Bay, Ishigaki Island, Japan.

To evaluate the relationships between coral calcification, thermal stress, and sedimentation and eutrophication linked to human impact (hereafter referred to as "land development") by river discharge, we analyzed growth characteristics in the context of a paleoenvironment that was reconstructed from geochemical signals in modern and fossil (1.2 cal kyr BP and 3.5 cal kyr BP, respectively) massive Porites corals from Nagura Bay ("Nagura") and from modern Porites corals from the estuary of the Todoroki River, Shiraho Reef ("Todoroki"). Both sites are on Ishigaki Island, Japan, and Nagura is located approximately 12 km west of Todoroki. At Nagura, the individual corals provide time windows of 13 (modern), 10 (1.2 cal kyr BP), and 38 yr in length (3.5 cal kyr BP). Here, we present the coral annual calcification for Nagura and Todoroki, and (bi) monthly resolved records of Sr/Ca (a proxy of sea surface temperature (SST)) and Ba/Ca (a proxy of sedimentation and nutrients related to land development) for Nagura. At Nagura, the winter SST was cooler by 2.8°C in the 1.2 cal kyr BP, and the annual and winter SSTs in the 3.5 cal kyr BP were cooler by 2.6°C and 4.6°C, respectively. The annual periodicity of Ba/Ca in modern coral is linked to river discharge and is associated with land development including sugar cane cultivation. Modern coral calcification also has declined with SST warming and increasing Ba/Ca peaks in winter. However, calcification of fossil corals does not appear to have been influenced by variations in Sr/Ca and Ba/Ca. Modern coral growth characteristics at Nagura and Todoroki indicate that coral growth is both spatially and temporally influenced by river discharge and land development. At Nagura, our findings suggest that land development induces negative thermal sensitivity for calcification in winter due to sugar cane harvest, which is a specifically modern phenomenon.

Toward an integrated management plan of the Djoudj Park water resources: Senegal River mouth.

A new approach was needed to preserve the biodiversity of the Djoudj Park within a context marked by many constraints: drought, regulation of its hydrologic system, and anthropogenic pressure. The local management plan developed in this paper aims at the responsible management and fair distribution of the available water resources in the Djoudj Park to provide a balanced response to conservation issues and the growing needs of the local communities. The opposition between an administration determined to exercise its power and the confidence of local people weary of being stripped of their rights and cultural assets required the setting up of a consensual management plan. This plan would provide a means to determine the timing and the number of sluice gates to operate, based on an efficient command of the needs for water for each activity in the park and its surroundings. This tool will allow the park authority to take full cognizance of the needs and opinions of all interest groups but also their limits while keeping the essential functions of this wetland. It is also suggested that institutional and administrative reform be carried out to associate local populations in the definition and implementation of criteria for an integrated management of the Djoudj resources.