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- Connections between upwelling patterns and phytoplankton variability under different coastal regimes in SW Iberia PeninsulaPublication . Krug, Lilian; Silvano, Kathleen M.; Barbosa, Ana B.; Domingues, Rita B.; Galvão, Helena M.; Luis, Joaquim; Platt, Trevor; Relvas, Paulo; Sathyendranath, ShubhaThe region off southwestern Iberia (NE Atlantic) encompasses a wide variety of oceanographic regimes, including differently (geographic) oriented coastal areas impacted by upwelling, riverine inputs and submarine groundwater discharge, submarine canyons and seamounts, and open ocean waters, thereby potentially promoting zone-specific phytoplankton dynamics. Overall, this heterogeneous region is classified as being very sensitive to climate change, and climate-driven alterations (e.g., sea surface warming, changes in upwelling patterns and intensity) have been recently reported for the area. The present study aims to understand the contribution of upwelling to seasonal and interannual variability of coastal phytoplankton, using a remote sensing-based approach. Phytoplankton variability was evaluated using satellite-derived chlorophyll-a (Chl-a), as a proxy for phytoplankton biomass, and primary productivity (PP). Chl-a were obtained from merged SeaWiFS (Seaviewing Wide Field-of-view Sensor), MeRIS (Medium Resolution Imaging Spectrometer) and MODIS-Aqua (Moderate-resolution Imaging Spectroradiometer) sensors at Globcolour portal. PP data at 9.25 km resolution were derived from Eppley’s Vertically Generalized Production Model, based on SeaWiFS and MODIS-Aqua and available at the Ocean Productivity site. Upwelling intensity was estimated using the difference in sea surface temperature (SST) between off and nearshore zones. Advanced Very-High Resolution Radiometer (AVHRR) 4 km SST were obtained from Pathfinder database. Other phytoplankton environmental drivers, such as local (e.g., river flow) and global (e.g., North Atlantic Oscillation - NAO) climate variables, were also analysed. The study area was divided into subareas differently impacted by upwelling and riverine flow, and satellitederived data was averaged for each zone. Seasonal and interannual variability covering a 14-year time series (1998- 2011) for each variable/region were explored. Chl-a at offshelf locations was significantly lower than coastal areas, and exhibited a fairly stable unimodal annual cycle, with maximum during March. Coastal locations displayed more variable annual patterns, with spring and summer Chl-a maxima, reflecting the impact of upwelling events and freshwater inputs. In respect to interannual variability, NAO index and coastal Chl-a were negative and significantly correlated, with 1-month lag. Chl-a interannual trends were also correlated to local climate variables, namely riverine flow for the easternmost coastal zone. The correlation between upwelling intensity and phytoplankton off SW Iberia is region-dependent being less strong within regions dominated by riverine influence.
- Reevaluation of magnetic chrons in the North Atlantic between 35 degrees N and 47 degrees N: implications for the formation of the Azores Triple Junction and associated plateauPublication . Luis, Joaquim; Miranda, J. M.In this paper we present a new magnetic compilation for an area of the North Atlantic located between 35 degrees N and 47 degrees N and up to anomaly 33r. We also present a strategy to pick magnetic isochrones and compute finite rotation poles. This technique is based on a continuous reduction to the pole technique and some basic assumptions regarding the direction of the remanent magnetization vector. A cost function that measures the misfit between interpreted and rotated isochrones and the systematic exploitation of the parameter space is used to compute the best set of finite Eulerian rotations for the chrons 5, 6, 6C, 11-12, 13, 18, 20, 21, 22, 23, 24, 25, 26, 28, 29, 30, 32, 33, and 33r. This set of chrons and poles is used to discuss the evolution of the North Atlantic close to Iberia and, in particular, the onset and early development of the Azores Triple Junction area. We show that the relative motion between the Eurasian and the African plates can be coherently described in terms of rigid plate kinematics, respecting both the anomalies shapes and the precise location of the main structural elements of the area: the Pico Fracture Zone, the East Azores Fracture Zone, and the Gloria Fault. We distinguish from the magnetic point of view two different areas of the Azores plateau: the South Azores domain where almost undisturbed NNW magnetic lineations can be found and the Azores domain close to the topographic highs and with no systematic magnetic stripping with the exception of a few recent lineations, probably Matuyama and Brunhes. We present an approximate reconstruction of the plate configuration after chron 18 to conclude that the attachment of Iberia to Eurasia was younger than previously thought (lower Miocene), triggering the formation of the Azores domain, in which stretching took place essentially in the last 20 Ma at an average rate of similar to 3.8 mm/a, and progressively attaching the South Azores domain to the African plate by a northward progression of the triple junction.