SIBER SPIS sept 2011.pdf - IMBER

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<strong>SIBER</strong> Science Plan and Implementation Strategy 2) What fraction of phytoplankton production is exported to the deep sea, and how are the benthic communities, and mid-water and benthic processes driven by this export How do these phenomena vary, with season, from abyssal plain to continental shelf, and between IO basins Export production and its influence on water column processes and benthic production, community structure and processes in the IO are also understudied and there is a need to carry out first-order descriptive science. The potential significance of benthic processes and benthic-pelagic coupling to marine biogeochemical cycling is established, but they remain poorly studied or quantified, especially in the IO. The extreme seasonal and/or spatial variability across the IO, in terms of primary production and oxygen depletion, give it wide-ranging importance with respect to global biogeochemical cycles, but also as a natural laboratory for benthic process studies. There is a primary need to quantify the fraction of primary production that is exported from the euphotic zone and in turn the portion of this export that is processed in the water column (and where). Quantification and characterization of the flux of organic matter that escapes pelagic recycling and is delivered to the sea floor are also required, as is assessment of the impacts on benthic communities in terms of biomass, diversity and activity patterns. Studies should address the degree to which regional variability in surface-ocean processes is mirrored in the deep sea, how particulate organic fluxes to continental margin and deep sea communities differ, and how the IO compares to other oceans in terms of variability in benthic communities and processes. What are the effects of pelagic food web processes and water column biogeochemistry (e.g. extent and intensity of oxygen depletion, denitrification and N 2 -fixation rates) on organic matter delivered to the sea floor The roles of benthic fauna and microbial processes (aerobic through methanogenesis) in the cycling and burial of carbon and other bioelements, and how these vary from the abyssal plain to the continental shelves, need to be clarified. It is also important to improve understanding of the nature and extent of benthic-pelagic coupling; how the benthos responds to pelagic forcing and, especially in shallow marginal environments, how benthic processes and associated sediment-water fluxes of dissolved gases, nutrients, organic matter and trace metals impact on the pelagic environment. How, on balance, do benthic solute fluxes serve in terms of sources or sinks in ocean inventories, and what influences do benthic fluxes and benthic-pelagic coupling have on productivity Ultimately, future studies should establish the wider biogeochemical significance of the processes and fluxes associated with export production and recycling (pelagic and benthic), and how these vary with season and across IO basins and marginal seas, with contrasting depth and hydrography, seasonal monsoon influence, riverine impacts and oxygen depletion. As discussed in Theme 3, the seasonal hypoxic zone over the western Indian shelf is the largest in the world, occupying an area of 0.2 x 106 km2. It is an order of magnitude greater than the better-known “dead zone” off the Mississippi mouth in the Gulf of Mexico (Naqvi et al., 2000). The presence of large and expanding coastal hypoxic zones has major implications for the large human populations living around the northern IO (e.g. with respect to water quality, fisheries resources, etc.). The presence of low-O 2 water also has profound impacts on benthic biogeochemical cycles and fluxes because it dramatically alters faunal composition and gives rise to chemical reactions like denitrification and anaerobic ammonium oxidation (anammox). Furthermore, the relative importance of pelagic versus sedimentary denitrification/anammox in the northern IO and the influence of varying O 2 concentrations on N cycling and redoxsensitive N fluxes (N 2 , NO 3 , NO 2 , NH 4 ) in the benthic boundary layer, need to be clarified. Also, studies are needed to assess the directions and magnitudes of benthic solute fluxes (gases, nutrients, DOM, DIC and metals) across IO margins, and how these relate to bottom water oxygen. 36
<strong>SIBER</strong> Science Plan and Implementation Strategy Th e m e 5: Cl i m a t e a n d a n t h r o p o g e n i c i m p a c ts o n t h e In d i a n Oc e a n a n d i t s m a r g i n a l s e a s How will human-induced changes in climate and nutrient loading impact the marine ecosystem and biogeochemical cycles Ba c k g r o u n d The latest IPCC AR4 report concluded that climate change is occurring and the most recent atmospheric CO 2 data show that atmospheric levels are increasing faster than even the most pessimistic projections used in the AR4 climate simulations (Raupach et al., 2007). It appears that both the rate of global warming and ocean acidification are accelerating. Further, many countries bordering the IO are experiencing rapid economic development (e.g. India and Australia), which will place greater strains on the terrestrial, coastal and marine environments. Given the expected future climate change and human development there is a pressing need to understand climate and anthropogenic impacts on the marine ecosystems of the IO and its marginal seas. Addressing this important issue will require improved understanding of marine ecosystems, targeted long-term observations to monitor and detect change, and mechanistic model simulations to investigate different impact scenarios. Recent research has documented a number of climate and anthropogenic impacts on IO ecosystems. Because of its rapid warming (International CLIVAR Project Office, 2006, Fig.14), the IO may provide a preview of how climate change will affect the biogeochemistry and ecology of other ocean basins and also human health. The observed warming trend in the Eurasian region over the past decade appears to have induced an increase in AS productivity (Goes et al., 2005). A new study suggests this warming trend will be amplified by the solar absorption caused by biomass burning and fossil fuel consumption (Ramanathan et al., 2007). The large-scale coral bleaching events of 1998 and 2005 highlight the susceptibility of the IO to warming and changes in ocean circulation (McClanahan et al., 2007). For instance, the 1998 bleaching event influenced higher trophic levels by altering the age distribution of commercially harvested fish (Graham et al., 2007). Coral reef ecosystems may be at greater risk than previously thought because of the combined effects of acidification, human development and global warming (Hoegh-Guldberg et al., 2007). These studies have started to explore climate and anthropogenic impacts on the IO, but much more research is needed to help mitigate the impacts and to assist adaptation to the changing environment. At the recent Asian Fisheries Forum (Kochi, 2007) there was widespread concern about the decrease in the mackerel population over the western continental shelf of India. It is assumed that the fish have moved to cooler, deeper waters beyond the shelf. This will cause far-reaching socioeconomic problems in the coastal states. There has also been a drastic decrease in the mackerel fishery in the last decade (CMFRI, Special Publication No. 98). With regard to river basins that drain into the IO there are several simultaneous developments that may have profound impacts on primary production, biodiversity and the carbon cycle, both in the coastal margins and the open ocean. First, the population of most countries proximal to IO river basins is increasing rapidly. Between 1970 and 2000 India’s population increased by more than 75% (UN, 2004). Together with economic growth this leads to a rapid increase in food production and a shift towards more protein-rich food such as meat and milk. The input of N and P fertilizers increased 7-8 fold between 1970 and 2000 (FAO, 2008) and has probably led to increased inputs to surface waters. FAO projections indicate that in the next three decades there will be a further 50% (N) to 80% (P) increase in fertilizer use in India (Bruinsma, 2003). Second, urbanization and the associated construction of sewage systems are promoting river nutrient export. This leads to rapidly increasing nutrient flows into surface water and eventually 37
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