Is the trend in chlorophyll- a in the Arabian Sea decreasing? (original) (raw)
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Variability in primary production as observed from moored sensors in the central Arabian Sea in 1995
Deep Sea Research Part II: Topical Studies in Oceanography, 1998
Carbon assimilation was calculated using surface irradiance and fluorescence data collected from moored sensors located in the Arabian Sea (15°30N, 61°30E), beginning the twelvemonth period in October 1994. The calculation uses an assumed quantum efficiency and independently estimated phytoplankton absorption coefficients. Fluorescence was calibrated to chlorophyll a. Estimated primary production (C assimilation) varied seasonally and was roughly correlated with chlorophyll a biomass. Variations in integral primary production estimated from the moored observations as a function of integral chlorophyll a are interpreted in terms of the variations in mixed layer depth and possible losses of chlorophyll a biomass. Deep mixed layers suggest lower chlorophyll a-specific production, and variations in chlorophyll a may indicate grazing losses. Seasonal variability in a measure of primary production is useful for establishing the relationship with environmental forcing in the Arabian Sea and in understanding the export of production to the deep sea.
Remote Sensing
Primary production by marine phytoplankton is one of the largest fluxes of carbon on our planet. In the past few decades, considerable progress has been made in estimating global primary production at high spatial and temporal scales by combining in situ measurements of primary production with remote-sensing observations of phytoplankton biomass. One of the major challenges in this approach lies in the assignment of the appropriate model parameters that define the photosynthetic response of phytoplankton to the light field. In the present study, a global database of in situ measurements of photosynthesis versus irradiance (P-I) parameters and a 20-year record of climate quality satellite observations were used to assess global primary production and its variability with seasons and locations as well as between years. In addition, the sensitivity of the computed primary production to potential changes in the photosynthetic response of phytoplankton cells under changing environmental ...
Detection of anthropogenic climate change in satellite records of ocean chlorophyll and productivity
Biogeosciences, 2010
Global climate change is predicted to alter the ocean's biological productivity. But how will we recognise the impacts of climate change on ocean productivity? The most comprehensive information available on its global distribution comes from satellite ocean colour data. Now that over ten years of satellite-derived chlorophyll and productivity data have accumulated, can we begin to detect and attribute climate change-driven trends in productivity? Here we compare recent trends in satellite ocean colour data to longer-term time series from three biogeochemical models (GFDL, IPSL and NCAR). We find that detection of climate change-driven trends in the satellite data is confounded by the relatively short time series and large interannual and decadal variability in productivity. Thus, recent observed changes in chlorophyll, primary production and the size of the oligotrophic gyres cannot be unequivocally attributed to the impact of global climate change. Instead, our analyses suggest that a time series of ∼ 40 years length is needed to distinguish a global warming trend from natural variability. In some regions, notably equatorial regions, detection times are predicted to be shorter (∼ 20 − 30 years). Analysis of modelled chlorophyll and primary production from 2001-2100 suggests that, on average, the climate change-driven trend will not be unambiguously separable from decadal variability until ∼ 2055. Because the magnitude of natural variability in chlorophyll and primary production is larger than, or similar to, the global warming trend, a consistent, decadeslong data record must be established if the impact of climate change on ocean productivity is to be definitively detected.
Marine primary production in relation to climate variability and change
Annual review of marine science, 2011
Marine photosynthetic plankton are responsible for approximately 50 petagrams (10(15)) of carbon per year of net primary production, an amount equivalent to that on land. This primary production supports essentially all life in the oceans and profoundly affects global biogeochemical cycles and climate. This review discusses the general distribution of primary production in the sea, the processes that regulate this distribution, and how marine primary production is sensitive to climate variability and change. Statistical modes of ocean variability and their characteristic interannual to multi-decadal timescales over the last century are described. Recent in situ and satellite time-series of primary production can be clearly linked to interannual ocean variability. Global marine primary production appears to have increased over the past several decades in association with multi-decadal variations. A paleoclimate record extends discussion to the centennial scale, providing contrasting ...
Interannual changes of the Arabian Sea productivity
Marine Biology Research, 2012
Inter-annual changes in temperature and chlorophyll a across the Arabian Sea (subdivided into 61 2-degree regions) were analysed. For each 2-degree region, from appropriate databases, remotely sensed chlorophyll a, sea surface temperature, and wind speed time series were retrieved. Spatial and temporal trend analysis showed physicalÁbiological oscillations with dominant periods of 12 and 6 months (reflecting the seasonality of monsoonal winds) with a globally warming trend, but no overall increase in chlorophyll during the period 1997Á2009. Variation coefficients of the inter-annual time series of chlorophyll a implied high variability in western regions of the sea in comparison to eastern regions. The basin-wide maps of chlorophyll distribution did not show the enlargement of the productive area over time and overall, not only did the Arabian Sea not get more productive, but several regions in its eastern basin showed a decline in chlorophyll a concentration.
Primary productivity and its regulation in the Arabian Sea during 1995
Deep-sea Research Part Ii-topical Studies in Oceanography, 2001
The annual cycle of monsoon-driven variability in primary productivity was studied in 1995 during the Arabian Sea Expedition as part of the United States Joint Global Ocean Flux Studies (US JGOFS). This paper describes the seasonal progression of productivity and its regulation on a section which ran from the coast of Oman to about 1000 km o!shore in the central Arabian Sea at 653E. During the SW Monsoon (June}mid-September), the coolest water and highest nutrient concentrations were close to the coast, although they extended o!shore to about 800 km; during the January NE Monsoon, deep convective mixing provided nutrients to the mixed layer in the region 400 } 1000 km o!shore. As expected, the SW Monsoon was the most productive season (123$9 mmol C m\ d\) along the southern US JGOFS section from the coast to 1000 km o!shore, but productivity in the NE Monsoon was surprisingly high (112$7 mmol C m\ d\). There was no onshore/o!shore gradient in primary productivity from 150 to 1000 km o! the Omani coast in 1995, and there was no evidence of light limitation of either primary productivity or photosynthetic performance (P ) from deep convective mixing during the NE Monsoon, deep wind mixing during the SW Monsoon or o!shore Ekman downwelling during the SW Monsoon. Productivity during the Spring Intermonsoon (86$6 mmol C m\ d\) was much higher than in oligotrophic regions such as the tropical Paci"c Ocean (29$2 mmol C m\ d\) or the North Paci"c gyre region (32$8 mmol C m\ d\).
Global ocean primary production trends in the modern ocean color satellite record (1998–2015)
Environmental Research Letters, 2019
Ocean primary production (PP), representing the uptake of inorganic carbon through photosynthesis, supports marine life and affects carbon exchange with the atmosphere. It is difficult to ascertain its magnitude, variability, and trends due to our inability to measure it directly at large scales. Yet it is paramount for understanding changes in marine health, fisheries, and the global carbon cycle. Using assimilation of ocean color satellite data into an ocean biogeochemical model, we estimate that global net ocean PP has experienced a small but significant decline −0.8 PgC y−1 (−2.1%) decade−1 (P
Global patterns of change and variation in sea surface temperature and chlorophyll a
Scientific reports, 2018
Changes over the scale of decades in oceanic environments present a range of challenges for management and utilisation of ocean resources. Here we investigate sources of global temporal variation in Sea Surface Temperature (SST) and Ocean Colour (Chl-a) and their co-variation, over a 14 year period using statistical methodologies that partition sources of variation into inter-annual and annual components and explicitly account for daily auto-correlation. The variation in SST shows bands of increasing variability with increasing latitude, while the analysis of annual variability in Chl-a shows mostly mid-latitude high variability bands. Covariation patterns of SST and Chl-a suggests several different mechanisms impacting Chl-a change and variance. Our high spatial resolution analysis indicates these are likely to be operating at relatively small spatial scales. There are large regions showing warming and rising of Chl-a, contrasting with regions that show warming and decreasing Chl-a...
As one of the major oceanic sinks of anthropogenic CO2, the Southern Ocean plays a critical role in the climate system. However, due to the scarcity of observations, little is known about physical and biological processes that control air-sea CO2 fluxes and how these processes might respond to climate change. It is well established that primary production is one of the major drivers of air-sea CO2 fluxes, consuming surface Dissolved Inorganic Carbon (DIC) during Summer. Southern Ocean primary production is though constrained by several limiting factors such as iron and light availability, which are both sensitive to mixed layer depth. Mixed layer depth is known to be affected by current changes in wind stress or freshwater fluxes over the Southern Ocean. But we still don't know how primary production may respond to anomalous mixed layer depth neither how physical processes may balance this response to set the seasonal cycle of air-sea CO2 fluxes. In this study, we investigate th...