CANOPO

CANOPO
the role of the Atlantic sector of the Southern Ocean in CO2 sequestration
Data Fisica Biogeochimica

The project intends to extend the dataset collected in the context of the ongoing ARGAU project, integrating its outcome with the results of numerical models. It is then important briefly describe the scientific objectives of ARGAU.
ARGAU is based on a collaboration between France and Argentina for the study of the long term variability of the CO2 air-sea fluxes in the South and Austral Atlantic. The rationale is that this area seems to be both a strong sink of Carbon for the atmosphere and a crucial area to identify changes due to the anthropogenic emission of CO2 in the atmosphere (Sarmiento, 1998). In order to be able to detect future changes, ARGAU has built a long term observational program (ten years) of in situ collected surface oceanic (SST, SSS, water CO2 partial pressure, alkalinity and phytoplankton biomass) and atmospheric (wind, humidity, heat fluxes) parameters.
The scientific objectives of ARGAU can be summarized as follows:

  1. estimate the space and time variability of the CO2 partial pressure in surface waters;
  2. identify the relative importance of the different trophic levels and of the different phytoplanktonic species on the air-sea flux of CO2;
  3. identify the role of the dynamical processes in the distribution of the different phytoplanktonic species and consequently in the variability of the air-sea flux of CO2;
The strategic importance of this project is due to the fact that the observations in the Austral Atlantic Ocean are very scarce, in spite of its important role in the global budget of the air-sea CO2 fluxes and in the global thermohaline circulation. On the other hand ARGAU in the present form does not include sub-surface measures and global modelling studies. The Italian contribution to ARGAU will cover those aspects thus improving the interpretation of the surface data collected during ARGAU by means the analysis of simultaneous subsurface and remote sensing data and with the aid of 1D and global 3D numerical models.
In particular we propose for CANOPO the following activities:
  1. collect vertical profiles of temperature from 0 to 700 m by means of XBT to monitor the water column for 3 years along the transect intersecting the Sub-Anctartic, the Polar Front and the meridional front of the ACC (see Fig.2);
  2. monitor the position of the Polar Front by means of altimeter data. The same analysis will be performed over a broad area including the Pacific sector (where similar measurements are collected in the frame of the CLIMA Italian project) ;
  3. study the correlation between the mixed layer depth, the variability of the surface fluxes (wind and E-P) and the CO2 fluxes, in the areas using a 1D ML model that will be coupled with 1D model of the CO2 evolution developed at LBCM;
  4. study the ML water mass dispersal (water paths and typical transport times) by means of lagrangian diagnostics applied to eulerian velocity fields from a 3D OGCM
  5. analyze the distribution of the biogeochemical tracers obtained via offline calculations using the same eulerian velocity field considered in the point 4;
  6. Estimate the interannual variability as described in the points 4 and 5 through forcing the model with the NCEP monthly surface fluxes from 1948 to 2000;
Vertical profiles of temperature (XBT). During the 4-month yearly cruise the ice-breaker A. Irizar, it will cross at least twice in open sea the Sub Antarctic and the Polar Front cruising from Argentina to South Otkey islands and twice the meridional front of the southern boundary of the ACC navigating from South Otkey islands Islands to the antarctic basis Belgrano(Fig.2), in the Southern Weddel Sea. The XBT will be launched in the 3 yearly cruises along the transects 1 or 1_bis and 2 identified in Fig.2 with a space resolution of 1/3 e di 1/6, far and near the thermal fronts, i.e. with a space resolution satisfying the WOCE standard.
The availability of simultaneous ARGAU surface data with data describing the evolution of the thermal structure of the water column up to intermediate depth will allow to establish the interplay between the dynamical processes linking the variability of the ML depth and fronts and the efficiency in the CO2 sequestration. The collected data will have also an intrinsic importance. In fact, the GCOS has outlined the priority (Smith and Nedleer 1995, Nowlin et al., 1996) of experimental measures allowing evidence of possible changes due to the anthropogenic activity. The Ocean has the potential for detecting climate change because integrating the large fluctuations on short time scales produces higher signal-to-noise ratio. Moreover a recent study (Banks and Wood 2002) show that the South and Austral Atlantic are an important place where anthropogenic climate change can be earliest detected, further remarking the importance of collection of subsurface data. We believe in the strategic importance of an Italian contribution devoted to the experimental monitoring of an important and scarcely known oceanic area. Moreover the collected of vertical profiles of temperature will be compared with similar measurements (Fig. 2a) obtained in the context of the GoodHope and CLIMA project. Finally the availability of in situ data will allow the validation of the 1D and 3D numerical model. During the cruises the Italian researchers will be freely lodged on the Argentinean ice-breaker A. Irizar. Possible transfers toward the Argentinean bases in Antartica will be in charge of the Argentinean Air Force.
Altimeter data The simultaneous analysis of altimeter data along tracks close to the Canopo and CLIMA (Fig. 2a) XBT transects will allow both a correct estimate of the Front position and orientation and a more detailed description of its time variability. Altimeter data will be obtained from TOPEX/POSEIDON, JASON and RA-2.
1D Mixed Layer model and atmospheric forcing. The study of the variability of the mixed layer depth as a function of the atmospheric forcing, is an important factor in estimating the variability of the absorption of the CO2 by the ocean. The 1D ML model will be validated with the temperature profiles from the XBT and it will be coupled with a 1D model of the CO2 concentration developed at LBCM.
Lagrangian diagnostics on the 3D OGCM This research activity will be done in close collaboration with the LODYC, based in Paris, France, using lagrangian analysis tools commonly used at ENEA and LODYC. Lagrangian diagnostics allow to identify water mass paths with related typical times of transport. In the case of water formed in the area like AAIW it will then possible to predict the site where the water masses rich in CO2 or with a specific bio-geochemical signature (e.g., Si/N, Dugdale and Wilkerson 1998) do surface. This Lagrangian diagnostics will first be applied to a reference experiment in which a standard implementation of the model is forced with climatologic surface fluxes, then to 4 different simulation in order to study the sensitivity of the water masses formation on the mixing processes and on the wind stress intensity and finally to an experiment in which the model is forced using the NCEP surface fluxes from 1948 to 2000.
Bio-geochemical models The local CO2 cycle and its link between the air-sea CO2 exchange in the Southern Ocean and the global CO2 cycle will be studied by analysing outputs from a global bio-geochemical model, PISCES, developed at LODYC. To date, PISCES has twenty-six compartments. There are five modeled limiting nutrients for phytoplankton growth: Nitrate and Ammonium, Phosphate, Silicate and Iron. Four living compartments are represented: two phytoplankton size-classes/groups corresponding to nanophytoplankton and diatoms, and two zooplankton size classes which are microzooplankton and mesozooplankton. There are three non-living compartments: semi-labile dissolved organic matter, small and big sinking particles. The iron, silicon and calcite pools of the particles are explicitly modeled. In addition to the ecosystem model, PISCES also simulates dissolved inorganic carbon, total alkalinity and dissolved oxygen. All the non-living compartments experience aggregation due to turbulence and differential settling. Following the dynamical process studies, the impacts of both subgrid-scale (eddies, vertical turbulence) and large-scale dynamics on the carbon-cycle will be investigated focusing on the three test sites of the Southern Ocean. In addition to the local responses to the physical forcing, the relationships between the Southern Ocean and the other ocean basins will be examined. A key question that will be addressed in this project is whether anomalies in the biogeochemical cycles generated in the Southern Ocean remain confined or whether they impact other regions of the world ocean.
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Programma Nazionale di Ricerche in Antartide

Enea - Progetto Speciale Clima Globale

Università degli Studi di Napoli 'Parthenope'

Stazione Zoologica 'Anton Dohrn'