Biomass changes and trophic amplification of plankton in a warmer ocean.

Ocean warming can modify the ecophysiology and distribution of marine organisms, and relationships between species, with nonlinear interactions between ecosystem components potentially resulting in trophic amplification. Trophic amplification (or attenuation) describe the propagation of a hydroclimatic signal up the food web, causing magnification (or depression) of biomass values along one or more trophic pathways. We have employed 3-D coupled physical-biogeochemical models to explore ecosystem responses to climate change with a focus on trophic amplification. The response of phytoplankton and zooplankton to global climate-change projections, carried out with the IPSL Earth System Model by the end of the century, is analysed at global and regional basis, including European seas (NE Atlantic, Barents Sea, Baltic Sea, Black Sea, Bay of Biscay, Adriatic Sea, Aegean Sea) and the Eastern Boundary Upwelling System (Benguela). Results indicate that globally and in Atlantic Margin and North Sea, increased ocean stratification causes primary production and zooplankton biomass to decrease in response to a warming climate, whilst in the Barents, Baltic and Black Seas, primary production and zooplankton biomass increase. Projected warming characterized by an increase in sea surface temperature of 2.29 ± 0.05 °C leads to a reduction in zooplankton and phytoplankton biomasses of 11% and 6%, respectively. This suggests negative amplification of climate driven modifications of trophic level biomass through bottom-up control, leading to a reduced capacity of oceans to regulate climate through the biological carbon pump. Simulations suggest negative amplification is the dominant response across 47% of the ocean surface and prevails in the tropical oceans; whilst positive trophic amplification prevails in the Arctic and Antarctic oceans. Trophic attenuation is projected in temperate seas. Uncertainties in ocean plankton projections, associated to the use of single global and regional models, imply the need for caution when extending these considerations into higher trophic levels.

A numerical study of the interannual variability of the Adriatic Sea (2000-2002).

A free-surface, three-dimensional finite-difference numerical model based on the Princeton Ocean Model (POM) has been implemented in order to simulate the interannual variability of the Adriatic Sea circulation. The implementation makes use of an interactive surface momentum and heat flux computation that utilizes the European Centre for Medium-Range Weather Forecasts (ECMWF) 6-h analyses and the model predicted sea surface temperatures. The model is also nested at its open boundary with a coarse-resolution Mediterranean general circulation model, utilizing the same surface forcing functions. The simulation and analysis period spans 3 years (1 Jan 2000 to 31 Dec 2002) coinciding with the "Mucilage in the Adriatic and the Tyrrhenian" (MAT) Project monitoring activities. Model results for the simulated years show a strong interannual variability of the basin averaged proprieties and circulation patterns, linked to the atmospheric forcing variability and the Po river runoff. In particular, the years 2000 and 2002 are characterized by a weak surface cooling (with respect to the climatological value) and well-marked spring and autumn river runoff maxima. Conversely, 2001 is characterized by stronger wind and heat (autumn cooling) forcings but no river runoff autumn peak, even though the total amount of water inflow during winter and spring is sustained. The circulation is characterized by similar patterns in 2000 and 2002 but very different structures in 2001. During the latter, deep water is not formed in the northern Adriatic. A comparison with the observed data shows that the major model deficiencies are connected to the low salinity of the waters, probably connected to the missed inflow of salty Ionian waters of Aegean origin and to the numerical overestimation of the vertical mixing processes.

Interannual variability of surface heat fluxes in the Adriatic Sea in the period 1998-2001 and comparison with observations.

Surface heat fluxes of the Adriatic Sea are estimated for the period 1998-2001 through bulk formulae with the goal to assess the uncertainties related to their estimations and to describe their interannual variability. In addition a comparison to observations is conducted. We computed the components of the sea surface heat budget by using two different operational meteorological data sets as inputs: the ECMWF operational analysis and the regional limited area model LAMBO operational forecast. Both results are consistent with previous long-term climatology and short-term analyses present in the literature. In both cases we obtained that the Adriatic Sea loses 26 W/m2 on average, that is consistent with the assessments found in the literature. Then we conducted a comparison with observations of the radiative components of the heat budget collected on offshore platforms and one coastal station. In the case of shortwave radiation, results show a little overestimation on the annual basis. Values obtained in this case are 172 W/m2 when using ECMWF data and 169 W/m2 when using LAMBO data. The use of either Schiano's or Gilman's and Garrett's corrections help to get even closer values. More difficult is to assess the comparison in the case of longwave radiation, with relative errors of an order of 10-20%.