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Variations in carbonate flux and dissolution, which occurred in the equatorial Atlantic during the last 24,000 years, have been estimated by a new approach that allows the point-by-point determination of paleofluxes to the seafloor. An unprecedented time resolution can thus be obtained which allows sequencing of the relatively rapid events occurring during deglaciation. The method is based on observations that the flux of unsupported 23øTh into deep-sea sediments is nearly independent of the total mass flux and is close to the production rate. Thus excess 23øTh activity in sediments can be used as a reference against which fluxes of other sedimentary components can be estimated. The study was conducted at two sites (Cear• Rise; western equatorial Atlantic, and Sierra Leone Pdse; eastern equatorial Atlantic) in cores raised from three different depths at each site. From measurements of 2aøTh and CaCOa, changes in carbonate flux with time and depth were obtained. A rapid increase in carbonate production, starting at the onset of deglaciation, was found in both areas. This event may have important implications for the postglacial increase in atmospheric CO2 by increasing the global carbonate carbon to organic carbon rain ratio and decreasing the alkalinity of surface waters (and possibly the North Atlantic Deep Water). Increased carbonate dissolution occurred in the two regions during deglaciation, followed by a minimum during mid-Holocene and renewed intensification of dissolution in late Holocene. During the last 16,000 years, carbonate dissolution was consistently more pronounced in the western than in the eastern basin, Copyright 1990 by the American Geophysical Union. Paper number 90PA01653. 0883-8305/90/90PA-01653510.00 reflecting the influence of Antarctic Bottom Water in the west. This trend was reversed during stage 2, possibly due to the accumulation of metabolic CO2 below the level of the Romanche Fracture Zone in the eastern basin. tivity [e.g., Broecker, 1982; Sarnthein et al., 1988; Mix, 1989] or for an increase in alkalinity of surface waters [e.g., Boyle, 1988; Broecker and Peng, 1989] during glacial periods. Different scenarios have been suggested which could account for such changes in the carbonate chemistry of seawater. They generally fall into two categories. One calls for changes in the carbonate chemistry of surface waters in polar oceans [Sarmiento and Toggweiler, 1984; Siegenthaler and Wenk, 1984; Knox and McElroy, 1984; Boyle, 1986; Broecker and Peng, 1989]. The other argues that low-latitude upwellings could play a major role [Newell et al., 1978; Flohn, 1982; Siegenthaler and Wenk, 1984; Boyle, 1986; Barnola et al., 1987; Sarnthein et al., 1987, 1988], especially if coupled with a change in the overall organic carbon to carbonate rain ratio [Berger and Keir, 1984; Dymond and Lyle, 1985]. The high-latitude by-1985.

SummaryBlack carbon (BC) found in ocean sediments provides regional and global information regarding biomass burning activities and transport mechanisms. BC fluxes to surface sediments, largely from the Pacific Ocean, range between 0.002-3.6 Ilg BC cm" yr" for deep sea sediments and 26-354 Ilg BC cm ., y{' for continental margin sediments. The BC flux may be a function of the magnitude of biomass burning, the distance to the source region, and riverine and eolian transport mechanisms.This manuscript presents some initial calculations of the global BC cycle. Using BC sediment flux data, we calculate global BC deposition to sediments in the deep ocean and continental margins, and compare these values to atmospheric deposition of BC to the global open and coastal ocean surface based on atmospheric BC concentration fields. About lOA Tg BC y{' are deposited in ocean sediments, largely in the coastal ocean. BC deposition to the ocean surface is much more homogeneous throughout the ocean, accounting for deposition of 6.9 Tg BC yr". We hypothesize that rivers may transport 12.2 Tg BC y{' to the ocean and that these particulates are largely deposited in coastal ocean sediments. The manuscript discusses gaps in our knowledge of sedimentary BC and suggests future research initiatives that might further understanding of the global cycle and temporal distribution in ocean sediments of this product of biomass burning.

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The Lancang-Mekong River has attracted much attention from researchers, but the cooperation on water issues in this river basin has been limited, even after the establishment of the Mekong River Commission (MRC). Cooperation on water resources has been determined as one of the key priority areas in the Lancang-Mekong Cooperation Mechanism, but there are no details of targets. In order to establish the priorities of water cooperation under the mechanism, we adopted nine categories to classify the objectives of 87 water cooperation events based on the 'Lancang-Mekong Water Cooperative Events Database' from 1995 to 2015. Based on the occurrence of cooperative events, cooperative objectives, cooperative scales, and approaches to cooperation, we conducted statistical, correlation, and text analyses. Our analyses indicated the following results: under the impact of economic conditions inside and outside the river basin, full cooperation appeared more difficult than bilateral and multilateral cooperation. Each of the partners adopted different preferences for cooperation targets. Cooperation with more definite objectives was easier to establish than cooperation with broader and more complex objectives. The potential objectives for water cooperation were navigation, hydropower, joint management, data sharing, flood control and water use. Because hydropower development is controversial, and because water cooperation is avoided by most existing regional cooperation mechanisms due to its complexity, we suggest the following priority areas for water cooperation in the Lancang-Mekong River Basin. 1) Navigation and flood control/drought relief are attractive objectives for all the riparian countries across the whole watershed. 2) Data sharing should be a priority for cooperation in the watershed due to its laying the foundation for the equitable and reasonable utilization of transboundary waters. 3) Hydropower is an objective best implemented mainly through bilateral cooperation, and on tributaries.

Marine protected areas (MPAs) are a key tool for achieving goals for biodiversity conservation and human well-being, including improving climate resilience and equitable access to nature. At a national level, they are central components in the U.S. commitment to conserve at least 30% of U.S. waters by 2030. By definition, the primary goal of an MPA is the long-term conservation of nature; however, not all MPAs provide the same ecological and social benefits. A U.S. system of MPAs that is equitable, well-managed, representative and connected, and includes areas at a level of protection that can deliver desired outcomes is best positioned to support national goals. We used a new MPA framework, The MPA Guide, to assess the level of protection and stage of establishment of the 50 largest U.S. MPAs, which make up 99.7% of the total U.S. MPA area (3.19 million km2). Over 96% of this area, including 99% of that which is fully or highly protected against extractive or destructive human activities, is in the central Pacific ocean. Total MPA area in other regions is sparse – only 1.9% of the U.S. ocean excluding the central Pacific is protected in any kind of MPA (120,976 km2). Over three quarters of the non-central Pacific MPA area is lightly or minimally protected against extractive or destructive human activities. These results highlight an urgent need to improve the quality, quantity, and representativeness of MPA protection in U.S. waters to bring benefits to human and marine communities. We identify and review the state of the science, including focal areas for achieving desired MPA outcomes and lessons learned from places where sound ecological and social design principles come together in MPAs that are set up to achieve national goals for equity, climate resilience, and biodiversity conservation. We recommend key opportunities for action specific to the U.S. context, including increasing funding, research, equity, and protection level for new and existing U.S. MPAs.

The Venice Lagoon (VL) is a complex ecosystem in which public participation and area-based management has often been neglected by administrative bodies involved in the planning of coastal projects and public works. In this area, the analysis of the local situation highlighted a substantial absence of coordination among the various administrative bodies in charge of planning and management at various governmental levels and in different regulated economic sectors. This paper analyses public participation and collaboration with reference to the Integrated Coastal Management context (ICM). The paper examines specific requirements, constraints, and opportunities for the complex case of the VL where participatory management and institutional coordination need enhancement.