ALBERT

Description: It is important to know how surface evapotranspiration and change in inundated areas are correlated, especially in flat Arctic wetlands such as the tundra region near Barrow, Alaska, as their underlying frozen ground and low hydrological gradient due to flat relief confine the lateral runoff of their standing water. Moreover, knowledge regarding seasonal dynamics of inundated areas is expected to be an essential and controlling factor in modeling regional energy and hydrological balance, which are related closely to frozen ground stability, in Arctic wetlands. However, the seasonal change and spatial distribution of inundated areas have not yet been well explored and quantified. Here we’ve deployed high spatial resolution (WorldView2 and QuickBird) images of Barrow area on eight dates from 2006-2014, to investigate seasonal change of inundated areas for a 4700 ha wetland, including the Barrow Ecosystem Observatory. Inundation dynamics were measured in the field in 2014 using DGPS. These ground truth data was used to develop a classification algorithm for discriminating between open water, overgrown water (mixed vegetation and standing water), and dry surfaces in the high-resolution images. The inundation index is created by combining NIR band, NDVI, and stack mean of BGR and NIR bands, and shown to be capable for mapping the extent of open water, dry, and overgrown water surfaces. In order to explore the relationship between water balance and changes in the inundated area, the estimated seasonal change in the inundated areas was compared with the daily surface water balance (rainfall – evaporation) calculated using available micrometeorological data for the years 2006-2014. Our results suggest that inundation dynamics correlated with the surface water balance during mid-late summer (July-September), though this relationship was not valid in the early summer (June), when surface hydrology is governed mainly by surface runoff above the shallow thawing front of the ground. With the inundation index developed and relationship between inundation index and surface water balance quantified in this study, it will become possible to automatically estimate inundation dynamics, which will improve our understanding of Arctic wetlands hydrology and support the scaling of local measurements to regional scales.

Description: A chlorophyll a hindcast in the Madeira Basin from 1871 to 2008 was used to analyze the long-term variability in the oligotrophic, subtropical gyres in relation to the climate change of the last century. The deep chlorophyll maximum (DCM), as dominant pattern of the chlorophyll a field, showed a fast decrease in its strength in the 1940s. An absolute minimum was reached between 1967 and 1973 when no DCM established with a recovering to the end of the time series. Long-term variability of the DCM was related to the North Atlantic Oscillation with a time delay of 9 years. The marked decrease in the 1940s was correlated to the drop of the solar radiation in transition from early brightening to global dimming. Caused by the influence of the solar radiation and maybe related to increasing global temperatures in the last century, the integrated chlorophyll a concentration decreased by about 0.7 mg m−2 in 2008 compared to 1871. The high-resolved chlorophyll a hindcast allowed an estimation of the carbon uptake by the ocean due to primary production in the euphotic zone. A rough calculation over the area of the global subtropical oceans showed 700 megaton less carbon uptake in 2008.