Search

The Southern Ocean regulates atmospheric CO2 and Earth's climate as a critical region for air‐sea gas exchange, delicately poised between being a CO2 source and sink. Here, we estimate how long a water mass has remained isolated from the atmosphere and utilize 14C/12C ratios (Δ14C) to trace the pathway and escape route of carbon sequestered in the deep ocean through the mixed layer to the atmosphere. The position of our core at the northern margin of the Southern Indian Ocean, tracks latitudinal shifts of the Southern Ocean frontal zones across the deglaciation. Our results suggest an expanded glacial Antarctic region trapped CO2, whereas deglacial expansion of the subantarctic permitted ventilation of the trapped CO2, contributing to a rapid atmospheric CO2 rise. We identify frontal positions as a key factor balancing CO2 outgassing versus sequestration in a region currently responsible for nearly half of global ocean CO2 uptake. Plain Language Summary: The Southern Ocean is a key region for the inhalation and exhalation of carbon dioxide, responsible for absorbing nearly half of the total amount of atmospheric c taken up by the modern global ocean. Today, regions of communication between the deep ocean and atmosphere are bounded by oceanographic fronts. During cold glacial periods, when sea ice cover expanded in the Southern Ocean, these regions were shifted northward. Our data shows that this northward movement pinched together the fronts in the Southern Indian Ocean, restricting glacial ocean‐atmosphere gas exchange, allowing CO2 to accumulate in the deep ocean. We find that at the end of the glaciation, the fronts returned southward and expanded, allowing transfer of the stored CO2 into intermediate and surface waters before escaping to the atmosphere. This trapping and releasing mechanism driven by frontal shifts is important for understanding how changes in Southern Ocean dynamics can affect the ability of the oceans to take up the additional atmospheric CO2 produced from human activities. Key Points: Indian Ocean Antarctic Intermediate Water was a pathway for ventilation of a deglacial carbon reservoirLatitudinal shifts in the Southern Ocean fronts contributed to glacial carbon storage and deglacial ventilationIntermediate waters of the Southern Indian Ocean were more than 2,000 years older in the deglaciation than the glacial and Holocene [ABSTRACT FROM AUTHOR]

The Luzon Strait (LS) hosts the largest transport of water between the Western Pacific Ocean (WPO) and the South China Sea (SCS). The transport through the strait, dominated by the westward propagation of the Kuroshio Intrusion, influences the climate and circulation of the SCS. While numerical models have investigated the interannual variability of the transport and subsequent water exchange across the LS, a lack of long‐term on‐site records prevents a general consensus on the transport rates, variability, and drivers. Corals offer high‐resolution, continuous histories of radiocarbon (Δ14C) content of the seawater dissolved inorganic carbon, allowing us to track changes in ocean transport and circulation through time. Seasonal and annual Δ14C samples from Houbihu, Taiwan, and Palaui, Philippines, located on either side of the strait, are compared to the Western Pacific Ocean and SCS Δ14C records to examine the spatial and temporal Δ14C variability in the region. We calculated the mean transport across the strait using a five‐box mixing model and identified its potential drivers. The mean amount of water exchanged across the strait from 1970 to 1999 was 2.2 Sv, ranging from −13.4 to 16 Sv, where a positive (negative) value indicates net flow into (out of) the SCS. A weaker East Asian Winter Monsoon increases the contribution of the SCS outflow on the Kuroshio Intrusion‐dominated LS, while the El Niño–Southern Oscillation primarily drives the intrusion into the SCS. These results provide support to the dominant control of El Niño–Southern Oscillation on the long‐term ocean circulation variability in this region. Plain Language Summary: The Luzon Strait is a globally critical ocean pathway that links the Western Pacific Ocean and the South China Sea (SCS). Heat, salt, and nutrients are exchanged across the strait, impacting marine ecology and climate in the region. In situ measurements of the surface water processes across the strait are limited, complicating our understanding of its variability and driving mechanism. Here, we present radiocarbon measurements, which represent a record of surface ocean processes including upwelling, extending beyond the instrumental record using two corals collected from either side of the strait, Houbihu, Taiwan, and Palaui, Philippines. Houbihu is impacted by the strength of the East Asian Winter Monsoon winds, affecting the transport of surface waters into and out of the SCS. Palaui is sensitive to surface transports linked to the shifts of the North Equatorial Current bifurcation latitude, primarily influenced by the El Niño–Southern Oscillation. While different processes impact our sites, the difference in the amount of radiocarbon between Houbihu and Palaui and the surrounding seas allows us to further investigate changes to water exchange across the strait. We find that a weaker East Asian Winter Monsoon impedes water inflow into the SCS whereas El Niño–Southern Oscillation facilitates inflow into the SCS. Key Points: Early bomb‐produced 14C spikes are evident in the Luzon Strait Δ14C recordsInterannual differences between our sites and other Δ14C records reveal basin‐specific processes controlling regional Δ14C variabilityENSO mainly drives the mean transport across the strait [ABSTRACT FROM AUTHOR]

Paired strontium-to-calcium (Sr/Ca) and d18O measurements for two Porites lutea corals recovered from Hon Tre Island, Vietnam, are strongly correlated to sea surface temperature (SST) and precipitation at monthly to interannual time-scales. Least squares linear regression of monthly Sr/Ca to SST shows a strong, significant correlation (r²=0.77, p<.0001), with root mean square residuals of 0.9°C. 3-year averaged (binned) Sr/Ca for wet (Sep-Nov) and dry (Jan-Mar) seasons separately captures SST variability at interannual time scales (Sr/Ca RMSR=0.42°C and 0.70°C for wet and dry seasons, respectively). Coral d18O correlates weakly to SST at seasonal and interannual time scales for wet and dry seasons, with significant anomalies (d18O RMSR=2.4°C and 1.65°C, respectively). Correcting the SST influence on coral d18O using paired Sr/Ca values provides estimates of d18O of seawater (d18Osw). 3-year averaged d18Osw during the wet season shows a significant correlation to local precipitation (r²=0.54, p=0.01). These results show that coral Sr/Ca in this location accurately reflects SST at a number of timescales, and that seawater d18O composition in the wet season is controlled by local precipitation, largely unmodified by ocean circulation during the winter monsoon. This study highlights the sensitivity and utility of coral geochemistry in this region for reliably reconstructing SST and monsoonal precipitation. [ABSTRACT FROM AUTHOR]

Environmental and human health challenges are pronounced in Asia, an exceptionally diverse and complex region where influences of global megatrends are extensive and numerous stresses to environmental quality exist. Identifying priorities necessary to engage grand challenges can be facilitated through horizon scanning exercises, and to this end we identified and examined 23 priority research questions needed to advance toward more sustainable environmental quality in Asia, as part of the Global Horizon Scanning Project. Advances in environmental toxicology, environmental chemistry, biological monitoring, and risk-assessment methodologies are necessary to address the adverse impacts of environmental stressors on ecosystem services and biodiversity, with Asia being home to numerous biodiversity hotspots. Intersections of the food-energy-water nexus are profound in Asia; innovative and aggressive technologies are necessary to provide clean water, ensure food safety, and stimulate energy efficiency, while improving ecological integrity and addressing legacy and emerging threats to public health and the environment, particularly with increased aquaculture production. Asia is the largest chemical-producing continent globally. Accordingly, sustainable and green chemistry and engineering present decided opportunities to stimulate innovation and realize a number of the United Nations Sustainable Development Goals. Engaging the priority research questions identified herein will require transdisciplinary coordination through existing and nontraditional partnerships within and among countries and sectors. Answering these questions will not be easy but is necessary to achieve more sustainable environmental quality in Asia. Environ Toxicol Chem 2020;39:1485-1505. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC., (© 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.)

Borehole density on the surface of Porites has been used as an indicator of water quality in the Great Barrier Reef. We assessed the relationship between borehole density on Porites and eight water quality parameters across 26 sites in Hong Kong. We found that total borehole densities on the surface of Porites at 16 of the studied sites were high (>1000individualsm(-2)), with polychaetes being the dominant bioeroders. Sedimentation rate was correlated positively with total borehole density and polychaete borehole density, with the latter relationship having a substantially higher correlation of determination. None of the environmental factors used were significantly correlated with bivalve borehole density. These results provide a baseline for assessing future changes in coral bioerosion in Hong Kong. This present study also indicates that polychaete boreholes can be used as a bioindicator of sedimentation in the South China Sea region where polychaetes are numerically dominant bioeroders., (Copyright © 2016 Elsevier Ltd. All rights reserved.)