Giulio Catalano

New observations of CO2-induced acidification in the northern Adriatic Sea over the last quarter century

Current global trends will lead to large-scale changes in climate patterns, ocean circulation and stratification; increased atmospheric CO2 levels will cause acidification of the oceans, with significant impacts on marine biogeochemical cycles and calcareous organisms. In the Mediterranean area, the northern Adriatic Sea is one of the most suitable sites for studying the responses of marine pH to such occurrences because it is the northernmost basin affected by dense water formation during winter, and is also one of the most productive areas in the Mediterranean. The first comparison between two sets of data relating to the dense cold waters of the northern Adriatic, formed in the winters of 1982–1983 and 2007–2008, is presented here. pH values on the Nation Bureau Standard scale from the old dataset have been converted to the ‘total hydrogen ion concentration scale’ adopted for the new dataset, and are expressed as μmol H . Results at 25 °C show acidification (−0.063 pHT units) and a decrease in carbonate ion concentration (−19.6 μmol H ) in the dense water mass between 1983 and 2008, whereas total alkalinity, carbonate alkalinity, dissolved inorganic carbon and CO2 fugacity exhibit net increases of 74.4, 77.8 and 110.3 μmol H , and 108.3 μatm, respectively, over the same period.

Nutrient balance in the ecosystem of the North Western Adriatic Sea

The effects of biological processes on dissolved inorganic nutrients, dissolved organic nitrogen (DON) and phosphorus (DOP) are considered in the north western Adriatic Sea. The budgets of these nutrients, which represent the sum of production and consumption processes in comparison to advection, are discussed with regard to dissolved inorganic nitrogen ( 15 N labelled) uptake, which basically indicates the biological demand of this fraction of nitrogen by phytoplankton community. The presented data show that, although important, the continental input of dissolved inorganic nitrogen (DIN), mainly nitrate, is utilised and recycled within the coastal marine environment (budget of m 15 r µmol-N·dm m 3 ). In fact, during four cruises (June, 1996; February, 1997; June, 1997; February, 1998), phytoplankton production was mainly driven by regenerated nutrients ( f h 0.4). Regarding dissolved inorganic phosphorus (DIP), the negative budgets observed in most cases (down to m 0.4 r µmol-P·dm m 3 ) confirm, above all, its scarce availability in this basin. Recycling processes rather than continental inputs regulate the availability of this nutrient. In addition, the comparison between DIN and DIP budgets indicates that, in this ecosystem, dissolved inorganic phosphorus is recycled faster than nitrogen through the living particulate and dissolved organic pools. As a consequence of biological activities, a strong production of dissolved organic nitrogen (DON) can occur in summer (up to +22 r µmol-N·dm m 3 ) while DOP shows a more independent behaviour both with respect to its accumulation in the environment and to the observed nitrogen variations.

Biogeochemistry and algal communities in the annual sea ice at Terra Nova Bay (Ross Sea, Antarctica)

During the fifteenth Italian Antarctic expedition, in the framework of the Pack Ice Ecosystem Dynamics programme, we investigated structure and functioning of the sympagic communities in the annual pack ice at Terra Nova Bay (74 °41.72′ S, 164 °11.63′ E). From November 1 to November 30 1999, we collected intact sea ice cores and platelet ice samples at an interval of 3 days. Ice samples were analysed for inorganic nutrients concentrations, algal biomass and productivity, pigment spectra, extracellular enzymatic activities and bacterial carbon production, micro-algal and metazoan community structure. Autotrophic biomass in the bottom ice increased more than two orders of magnitude from the beginning to the end of November 1999 (i.e. from c. 1–400 mg chlorophyll a m−3). In the same temporal interval, inorganic nutrients concentrations as well as dissolved organic matter sharply increased. Pigment spectra and microscopic analyses revealed that bottom ice communities were different from those of the platelet ice. The bottom-ice sympagic flora was represented almost exclusively by cryobenthic species, whereas platelet ice was characterised by the presence of both cryopelagic and cryobenthic species. Metazoan community in the bottom sea ice was largely dominated by copepods. In particular, the calanoiod Stephos longipes and the harpacticoid Harpacticus furcifer accounted for more than 90% of the sympagic fauna. In the bottom sea ice concentrations of phaeophorbides and other degraded phytopigments were low indicating that most of the sympagic flora was active. These findings suggest that grazing pressure might be only a minor factor controlling or regulating inorganic nutrient concentrations. Conversely, potential degradation rates of organic carbon mediated by extracellular enzymatic activity were very high and largely exceeded organic matter production by photosynthesis.

Spatial and Temporal Patterns of Nutrient Distributions in the Ross Sea

The Ross Sea is one of the most peculiar zones in the World Ocean because of its physical, chemical and biological characteristics. On its continental shelf, it is influenced by only one water mass of external origin, the Circumpolar Deep Water (CDW), which, in turn, generates all the other water types by cooling or mixing with water coming from ice melting. From the biological and chemical point of view, the Ross Sea is considered as a typical Continental Shelf Coastal Zone (CSCZ) where, during summer, occasional high nutrient consumption occurs particularly in the Marginal Ice Zone (MIZ) and in some protected coastal areas as Terra Nova Bay.

Nutrient depletions in the Ross Sea and their relation with pigment stocks

Abstract The present article depicts a first attempt to relate the governing nutrient uptake regime and phytopigment signature of the Ross Sea. Based on nutrient and phytopigment data obtained during two cruises in the Ross Sea, two distinct groups were recognised. The first one was characterised by moderate nutrient (nitrate and silicic acid) depletions in combination with relatively high diatom and Phaeocystis abundance. The second group showed very low nutrient depletions and very poor diatom abundance. Average depth specific nitrate depletions were 8.1 and 1.1 μM and average silicic acid depletions were 21.5 and 1.3 μM, respectively. The nutrient consumption patterns did not match the conditions of silicic acid excess (SEA) or nitrate excess areas (NEA), a clear trend being probably obscured by very poor seasonal maturity of several sampling stations. The contrast between both groups is largely explained by small differences in nitrogen uptake regime of the major phytoplankters. During early season, the diatoms meet the majority of their nitrogen requirements by nitrate uptake, with few exceptions where ammonium is the most important nitrogenous substrate. On average, their nitrate uptake capacity is lower than that of Phaeocystis (average specific nitrate uptake rates were 0.021 and 0.036 day −1 for diatoms and Phaeocystis , respectively). The latter phytoplankton always shows predominance of nitrate uptake. Both groups are subject to inhibition of nitrate uptake when ammonium availability increases, and it is likely that the diatoms are more sensitive to the inhibitory effect of ammonium.

The carbon budget in the northern Adriatic Sea, a winter case study

This paper presents a winter carbon budget for the northern Adriatic Sea, obtained through direct measurements during two multidisciplinary cruises and literature data. A box model approach was adopted to integrate estimates of stocks and fluxes of carbon species over the total area. The oligotrophy at the basin scale and the start of primary productivity well before the onset of spring stratification were observed. In winter, the system underwent a complete reset, as the mixing of water masses erased any signal of previous hypoxia or anoxia episodes. The northern Adriatic Sea was phosphorus depleted with respect to C and N availability. This fact confirms the importance of mixing with deep-sea water for P supply to biological processes on the whole. Despite the abundant prokaryotic biomass, the microbial food web was less efficient in organic C production than phytoplankton. In the upper layer, the carbon produced by primary production exceeded the fraction respired by planktonic community smaller than 200 µm. On the contrary, respiration processes prevailed in the water column below the pycnocline. The carbon budget also proved that the northern Adriatic Sea can be an effective sink for atmospheric CO2 throughout the entire winter season.

modeling approach of the Ross Sea plankton ecosystem

A conceptual and numerical model adapted to the local plankton ecosystem (ECOHYDROMVG) has been developed on the basis of the information acquired during various oceanographic cruises in the Ross Sea. The construction of the biological/physical coupled 1-D model of the upper water column ecosystem is presented. The model takes into account the control of the plankton ecosystem by ice cover, ice edge dynamics, atmospheric forcing and surface circulation, nutrients being non-limiting factors. Ice-edge thickness, retreat and melting determine the initial conditions for the spring bloom (ice algae concentration, vertical structure of the water column) and allow the biological processes of primary production in the water column to start. The combined effects of wind and solar irradiance determine the depth of the upper mixed layer and quantitatively control photosynthetic levels. In this approach, biological variables are limited to diatoms, Phaeocystis and smaller cells, depending on local conditions. Grazing activity forcing by Euphausia superba, copepods, Limacina helicina and amphipods control the phytoplankton variables. The model is used to determine a standard state of the Ross Sea plankton ecosystem and numerical results accurately simulate the vertical stabilization of the water column within the Ross Sea marginal ice zones during the ice-melting period, and the biological structure of the upper layers. It simulates primary production and the selection of the type of phyto- and zooplankton communities. It is applied to local situations controlled by different wind conditions, ice cover and initial content of ice algae, and accurately reproduces field observations.

Biological Utilisation of the Major Nutrients in the Western Coastal Waters of the North Adriatic Sea

The availability and distribution of the dissolved inorganic and organic fractions of nitrogen (DIN and DON) and phosphorus (DIP and DOP) are extremely variable in the north-western Adriatic Sea. Freshwater inputs, mainly from the Po River, and biological processes significantly affect the nutrient behaviour in this region. The purpose of this contribution is to describe these processes by the comparison of the dissolved nitrogen and phosphorus distributions to computed estimates of their biological production or consumption in the marine environment. The variations of dissolved nitrogen were mainly due to freshwater inputs of DIN, especially in winter (up to 18 μmol-N·dm−3), while a high marine release of DON was observed in summer (up to +22 μmol-N·dm−3 compared to the contribution of advection). The DIP concentrations were generally lower than 0.06 μmol-P·dm−3, while DOP values ranged from 0.01 to 0.1 μmol-P·dm−3. The evident inverse relationship between DIP and DOP behaviours indicated that the phosphorus availability in the coastal zone is mainly regulated by recycling processes rather than by terrestrial inputs.