Posts Tagged 'modeling'

Acidification mediated by a river plume and coastal upwelling on a fringing reef at the east coast of Hainan Island, Northern South China Sea

We investigated the dynamics of carbonate system which was greatly modulated by a river plume and coastal upwelling in July 2014 and July 2015 at the east coast of Hainan Island where a fringing reef distributes inshore. By using a three end-member mixing model, we semiquantitatively estimated the removal of dissolved inorganic carbon (DIC) mediated by biological production in the river plume and upwelled water to be 13 ± 17 and 15 ± 16 μmol kg−1, respectively. The enhanced organic production was mainly responsible for these DIC consumptions in both two regimes, however, nearly a half of DIC removal was attributed to biocalcification in the plume system while it was negligible in the upwelling system. Furthermore, the modeled results over reefs revealed that river plume and coastal upwelling were two major threats of acidification to coral communities at the east coast of Hainan Island during cruises. In comparison, the biological contribution to acidification was limited for balancing between organic production and biocalcification during July 2014 cruise, whereas the acidification was greatly intensified by organic degradation during July 2015 cruise. It was verified that naturally local acidification (physical and biological processes) played a major role in great pH decreases on a short-term scale, leading to coastal waters more vulnerable to anthropogenic “ocean acidification” (uptake of atmospheric CO2) by reducing buffering capacity of waters. Finally, effects of acidification associated with other local threats on a fringing reef were further depicted with a conceptual model.

Continue reading ‘Acidification mediated by a river plume and coastal upwelling on a fringing reef at the east coast of Hainan Island, Northern South China Sea’

Future marine ecosystem drivers, biodiversity, and fisheries maximum catch potential in Pacific Island countries and territories under climate change

Highlights

  • Under the RCP 8.5 scenario, tropical Pacific temperature will rise by ≥ 3 °C by 2100.
  • This is accompanied by declines in dissolved oxygen, pH, and net primary production.
  • This will lead to local extinctions of up to 80% of marine species in some regions.
  • 9 of 17 Pacific Island entities experience ≥ 50% declines in maximum catch potential.
  • Impacts can be greatly reduced by mitigation measures under the RCP 2.6 scenario.


Abstract

The increase in anthropogenic CO2 emissions over the last century has modified oceanic conditions, affecting marine ecosystems and the goods and services that they provide to society. Pacific Island countries and territories are highly vulnerable to these changes because of their strong dependence on ocean resources, high level of exposure to climate effects, and low adaptive capacity. Projections of mid-to-late 21st century changes in sea surface temperature (SST), dissolved oxygen, pH, and net primary productivity (NPP) were synthesized across the tropical Western Pacific under strong climate mitigation and business-as-usual scenarios. These projections were used to model impacts on marine biodiversity and potential fisheries catches. Results were consistent across three climate models, indicating that SST will rise by ≥ 3 °C, surface dissolved oxygen will decline by ≥ 0.01 ml L−1, pH will drop by ≥ 0.3, and NPP will decrease by 0.5 g m−2 d−1 across much of the region by 2100 under the business-as-usual scenario. These changes were associated with rates of local species extinction of > 50% in many regions as fishes and invertebrates decreased in abundance or migrated to regions with conditions more suitable to their bio-climate envelope. Maximum potential catch (MCP) was projected to decrease by > 50% across many areas, with the largest impacts in the western Pacific warm pool. Climate change scenarios that included strong mitigation resulted in substantial reductions of MCP losses, with the area where MCP losses exceeded 50% reduced from 74.4% of the region under business-as-usual to 36.0% of the region under the strong mitigation scenario.

Continue reading ‘Future marine ecosystem drivers, biodiversity, and fisheries maximum catch potential in Pacific Island countries and territories under climate change’

Assessment and management of cumulative impacts in California’s network of marine protected areas

In response to concerns about human impacts to coastal ecosystems, conservationists and practitioners are increasingly turning to networks of marine protected areas (MPAs). Although MPAs manage for fishing pressure, many species and habitats in MPAs remain exposed to a multitude of stressors, including stressors from global climate change and regional land- and ocean-based activities. To support the adaptive management of MPAs that are subject to multiple interacting stressors, coastal managers need to understand the potential impacts from other single and multiple stressors. To demonstrate how this can be done, we quantify and map cumulative impacts resulting from multiple stressors to California’s network of MPAs, using a widely available cumulative impacts mapping tool. Among individual stressors, those related to climate, including ocean acidification, UV radiation increases, and SST anomalies, were found to have the most intense impacts, especially on surface waters and in the rocky intertidal. Climate stressors are challenging to limit at the local MPA scale, but intense land- and ocean-based impacts that were found to affect a majority of MPAs, such as sediment increases, invasive species, organic pollutants and pollution from shipping and ports, may be more easily regulated at a regional or local scale. This is especially relevant for South and Central coast MPAs where these impacts are the greatest on beaches, tidal flats, and coastal marshes. Accounting for cumulative impacts from these and other stressors when developing monitoring and management plans in California and across the world, would help to improve the efficacy of MPAs.

Continue reading ‘Assessment and management of cumulative impacts in California’s network of marine protected areas’

Understanding the impacts of anthropogenic stressors on species, ecosystems, and fishing communities

Anthropogenic modifications of marine environments result from a variety of activities and have effects across social and ecological dimensions. Humans inhabit linked systems, where our actions such as resource extraction, pollution and development influence species in both direct and indirect ways and feedback to influence the human communities dependent on living marine resources. In order to understand the consequences of our actions and develop strategies to plan for future environmental change, we need a diverse set of tools able to incorporate various levels of complexity. This necessitates the improvement and modification of existing tools, development of novel approaches and unique applications of methods from across fields. In this dissertation I address the ways in which we can use and improve existing tools in ecology to advance our understanding and management of marine resources. In the first Chapter I introduce a method to incorporate life stage specific responses to a stressor, ocean acidification, to gain a broader understanding of population level vulnerability. In the second Chapter I extend this work to address ecosystem level change from ocean acidification in the California Current, using an ecosystem model to determine changes in biomass and fisheries catch. In the third chapter, I work to improve our understanding of how multiple stressors acting across life history can be magnified or mitigated, based solely on biological characteristics of populations. Finally, in the fourth Chapter I introduce ecologists and natural scientists to a broader understanding of research on risk in order to improve our methods for approaching ecosystem based fisheries management. My work spans ecological scales from populations to ecosystems and links between social and ecological systems.

Continue reading ‘Understanding the impacts of anthropogenic stressors on species, ecosystems, and fishing communities’

Numerical modeling of fish mortality at high CO2 concentrations representing acclimation

A mortality model was developed to predict the impact of high CO2 concentrations on marine fish. To allow for acclimation to a gradual increase of PCO2, the model includes acid–base regulation processes, such as respiration and ion-exchange at the gills. Because the physiological mechanism connecting a decrease in blood pH and mortality is not known, a statistical model was adopted. The mortality calculated for Japanese sillago experiencing a transient change of PCO2 compares moderately well with observations.

Continue reading ‘Numerical modeling of fish mortality at high CO2 concentrations representing acclimation’

The potential of 230Th for detection of ocean acidification impacts on pelagic carbonate production

Concentrations of dissolved 230Th in the ocean water column increase with depth due to scavenging and downward particle flux. Due to the 230Th scavenging process, any change in the calcium carbonate (CaCO3) fraction of the marine particle flux due to changes in biological CaCO3 hard shell production as a consequence of progressing ocean acidification would be reflected in the dissolved 230Th activity. Our prognostic simulations with a biogeochemical ocean general circulation model using different scenarios for the reduction of CaCO3production under ocean acidification and different greenhouse gas emission scenarios (RCPs 8.5 to 2.6) reveal the potential for deep 230Th measurements to detect reduced CaCO3 production at the sea surface. The time of emergence of an acidification induced signal on dissolved 230Th is of the same order of magnitude as for alkalinity measurements. Yet, deep ocean 230Th concentrations are less affected by seasonal and multiyear variability than surface alkalinity. Thus, deep ocean 230Th observations could be advantageous to guide monitoring and detection campaigns. Furthermore, given that the precision of 230Th measurements may potentially improve in the near future, earlier detection of ocean acidification impact signals would be possible. Our results indicate that the deep Pacific Ocean and the deep Southern Ocean are the most suitable regions for selected regular reoccupations of deep reaching 230Th stations.

Continue reading ‘The potential of 230Th for detection of ocean acidification impacts on pelagic carbonate production’

Inorganic carbon fluxes on the Mackenzie Shelf of the Beaufort Sea

The Mackenzie Shelf in the southeastern Beaufort Sea is a region that has experienced large changes in the past several decades as warming, sea-ice loss, and increased river discharge have altered carbon cycling. Upwelling and downwelling events are common on the shelf, caused by strong, fluctuating along-shore winds, resulting in cross-shelf Ekman transport, and an alternating estuarine and anti-estuarine circulation. Downwelling carries inorganic carbon and other remineralization products off the shelf and into the deep basin for possible long-term storage in the world oceans. Upwelling carries dissolved inorganic carbon (DIC) and nutrient-rich waters from the Pacific-origin upper halocline layer (UHL) onto the shelf. Profiles of DIC and total alkalinity (TA) taken in August and September of 2014 are used to investigate the cycling of inorganic carbon on the Mackenzie Shelf. The along-shore transport of water and the cross-shelf transport of inorganic carbon are quantified using velocity field output from a simulation of the Arctic and Northern Hemisphere Atlantic (ANHA4) configuration of the Nucleus of European Modelling of the Ocean (NEMO) framework. A strong upwelling event prior to sampling on the Mackenzie Shelf is analyzed and the resulting influence on the carbonate system, including the saturation state of waters with respect to aragonite and pH, is investigated. TA and the oxygen isotope ratio of water (δ18O) are used to examine water-mass distributions in the study area and to investigate the influence of Pacific Water, Mackenzie River freshwater, and sea-ice melt on carbon dynamics and air-sea fluxes of carbon dioxide (CO2) in the surface mixed layer. Understanding carbon transfer in this seasonally dynamic environment is key to quantify the importance of Arctic shelf regions to the global carbon cycle and provide a basis for understanding how it will respond to the aforementioned climate-induced changes.

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Ocean acidification in the IPCC AR5 WG II

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