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Rapid Assessment of the Marine Primary Productivity Trends in the Arctic Ocean and Its Surrounding Seas

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Rapid Assessment of the Marine Primary Productivity Trends in the Arctic Ocean and Its Surrounding Seas Rapid assessment of the marine primary productivity trends in the Arctic Ocean and its surrounding seas ACTUS inc. and WWF Final version March 2011 Table of Contents Abstract.............................................................................................................................................4 1. Introduction..................................................................................................................................5 2. Methodology.................................................................................................................................6 2.1. Satellite-based primary production estimation.....................................................................6 2.2. Statistical analysis.................................................................................................................7 2.2.1. Identification of the most productive pixels..................................................................7 2.2.2. Trend analysis ..............................................................................................................7 3. Results and discussion..................................................................................................................8 3.1. Pan-Arctic scale....................................................................................................................8 3.1.1. Total productivity..........................................................................................................8 3.1.2. Decadal trends.............................................................................................................11 3.2. Ecoregional scale................................................................................................................16 3.2.1. Overview of all ecoregions.........................................................................................16 3.2.2. Beaufort Sea – continental coast and shelf..................................................................23 3.2.3. Laptev Sea...................................................................................................................25 4. Conclusions................................................................................................................................27 Glossary..........................................................................................................................................30 References.......................................................................................................................................31 Appendix........................................................................................................................................34 List of Figures Figure 1: Yearly primary production rates estimated using 13 years SeaWiFS images .................9 Figure 2: Total annual primary production estimates during the SeaWiFS Era ............................11 Figure 3: Trends in PP calculated using the non parametric method proposed by Zhang et al. (2000). ..........................................................................................................................................12 Figure 4: Anomaly in total PP at the pan-arctic scale (black), and anomaly explained by OC variability alone (grey) and light available for photosynthesis alone (blue). ................................14 Figure 5: The relationship between the anomaly explained by OC and light availability. ...........14 Figure 6: Figure 6 - Monthly decompose PP anomaly at the pan arctic scale................................15 Figure 7: Total annual primary production estimates during the SeaWiFS era for each ecoregion considered by RACER....................................................................................................................19 Figure 8: Total annual primary production estimates during the SeaWiFS era for each ecoregion considered by RACER....................................................................................................................20 Figure 9: Total annual primary production estimates during the SeaWiFS era for each ecoregion considered by RACER....................................................................................................................21 Figure 10: PP production rates of the Beaufort Sea (continental coast and shelf).........................24 Figure 11: Monthly decomposed total PP time series of the Beaufort Sea ...................................25 Figure 12: PP trends of the Beaufort Sea computed using TSA.....................................................26 Figure 13: PP production rates of the Laptev Sea..........................................................................27 Figure 14: Monthly decomposed total PP time series of Laptev Sea for all pixels (blue) and the 10% most productive pixels (black). .............................................................................................28 Figure 15: PP trends of the Laptev Sea computed using TSA. Only pixels with significant trend (90% confidence level) are plotted.................................................................................................29 2 List of Tables Table 1: Comparison between satellite derived PP rates and published PP rate by Sakshaug 2004 (His table 3.7).................................................................................................................................10 Table 2: Summary of the statistics of the mean annual PP rates (gC m-2 y-1) of each ecoregion. ........................................................................................................................................................16 Table 3: Main drivers controlling the inter-annual variability of total annual PP for each ecoregion. .......................................................................................................................................18 Table 4: Trend analysis for each ecoregion following the Zhang et al. (2000) method.................22 3 Abstract A 13-years time series of SeaWiFS imagery was employed to estimate the primary productivity (PP) rates taking place in the Arctic Ocean and its surrounding seas. The objective is to identify regions of biological interest and to assess how they are responding to the recent climate changes. A semi-analytic PP model ingesting satellite observations of cloud cover, sea ice concentration (SIC) and ocean inherent optical properties as determined ocean color (OC) measurements were employed to assess PP in both phytoplankton-dominated and colored dissolved organic matter (CDOM)-dominated waters. A preliminary validation suggested that the model produced PP rates within the range observed in situ over the arctic interior shelves, but may be underestimating PP in other regions. Unlike the previous satellite-based PP estimates, our model shows realistic estimates over the continental shelves supporting the necessity of using semi-analytical approaches to estimate both chlorophyll-a (CHL) concentration and diffuse attenuation coefficient to minimize the CDOM contamination. Hot-spots of high productivity, identified at the ecoregional scale, were found in areas influenced by large arctic rivers, in the marginal ice zone, at shelf breaks or in straits. A statistically significant trend in the temporal variation of PP was found at the pan-arctic scale (5.05 Tg C y-1). To explain the sources of this variation, the PP model was run several times with different input parameters set as constant. It was found that the main parameter that controlled the temporal trend reported above was the changes in OC (2.88 Tg C y-1). The second most important parameter (1.1 Tg C y-1) was SIC which incorporates light availability for photosynthesis through measurements of the shrinking of the sea ice cover. The ecoregional trends analysis indicates that both type of changes (OC versus SIC) operate in different proportions among regions. In general, increasing light availability explained most of the increase in PP over the arctic interior shelves, while changes in biomass are responsible for the increase in PP in permanently open waters. Although positive trends were observed in most ecoregions, significant negative trends were also observed in regions that are normally recognized for their great biological importance. This is the case with the North Water Polynya in the Canadian Arctic where the decrease in PP reaches as much as 5.6 gC m-2 y-1, corresponding to a >100% relative decrease in PP over 13 years. These results suggest that major environmental changes, yet not well understood, can locally have negative impacts on the marine ecosystem productivity. Finally, a more detailed analysis at ecoregional scale was exemplified at two ecoregions : the Beaufort Sea - continental coast and shelf and the Laptev sea. 4 1. Introduction This study takes place as part as RACER – a project of WWF’s Global Arctic Program that seeks to identify important places in the Arctic in the face of rapid climate change. RACER stands for Rapid Assessment of features and areas for Circum-arctic Ecosystem Resilience in the 21st Century. The ultimate goal of RACER is to develop the analyses that will identify some of the key places that will remain important for the well-being of Arctic ecosystems and human communities as we experience climate change. The RACER premise has been that if such places can be identified and given conservation attention when making decisions on land
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