A collaborative project in coastal oceanography

The AMICO-BIO project is an interdisciplinary project co-funded by the French Ministry of the Environment, the CNRS-INSU and LEFE-GMMC. It aims to investigate the effects of different implementations of open boundary conditions (OBCs) on regional 3D biogeochemical ocean models. The project is focused on 2 main study areas: (1) the Bay of Biscay (NE Atlantic) and (2) the Gulf of Lion (NW Mediterranean).

study area
Scientific rationale and socio-economic context

There are many known applications for Operational Coastal Oceanography, including maritime safety, navigation, management of fish stocks and marine parks, marine renewable energy, risks related to environmental protection and water quality for bathing and aquaculture, etc.. Furthermore, in order to improve our understanding and our capacity to analyze and forecast processes in coastal environments, we need to take into account the inherent complexity and particularities associated with coastal oceans:

  • A strong influence of the bathymetry and land (geometric constraints affecting currents, continental inputs by rivers, etc.)
  • The interplay of a large number of physical forcing factors (tides, wind, internal waves, wave induced circulation ...)
  • The interplay of high frequency dynamics of both local and large-scale atmospheric origin with the low frequency (seasonal) variability
  • Small scale processes (tidal fronts and plume dynamics, internal tide, solitary waves, extremely sharp and strong thermoclines)
  • A strong heterogeneity of ecosystems and substrate (sediment and benthic habitats).
Unlike the open ocean, coastal phenomena are often highly complex and interdependent and therefore require a highly interdisciplinary approach.

The numerical modeling of pelagic plankton ecosystems is a vast area of research that has seen a large growth since the 1980’s, largely associated with an equally rapid growth and easy availability of computing power. A vast array of different models has evolved which exhibit great differences in model architecture and complexity that range from simple NPZD models to highly complex and compartmentalized global models featuring several different planktonic functional groups.
Coastal models allow users to zoom in on areas of particular interest and examine processes which are often not represented in global models. For the successful implementation of regional configurations it is crucial, however, to apply a system of downscaling to the global coupled physical and biogeochemical models typically provide forcing to the regional models at the open boundaries.

The aim of the current project is to facilitate the development of a continuum approach between the coastal and global ocean models in order to improve the ability of different types of models to communicate with one another, especially with regard to improve the representation of the continuum of scales and processes between the open and coastal oceans. In particular, we focus on the improvement of the physical-biogeochemical coupling in regional scale models. There are still many unresolved issues in this field of research. AMICO-BIO provides a first step towards addressing some of these issues. In France, several operational global-scale coupled physical-biogeochemical models are being operated by Mercator while regional models are operated by Prévimer. However, they remain unconnected with one another. One of the inherent difficulties in coupling global with regional-scale models is related to the fact that the global model, which provides the external forcing at the open boundaries of the regional models, has different inherent model dynamics than the regional model which then leads to poor results at those boundaries. methodology This problem can be so severe, that in order to avoid it, many coastal modellers currently use what could be described as an “internal forcing mode” with zero gradients, or they deploy their coastal model at the global scale in order to avoid incompatibility problems, but at the expense of a much increased computational effort. AMICO-BIO aims to provide a major advancement in this area of research by examining the various ways in which the forcing obtained from global scale models can be applied to the open boundaries of regional models. The operational teams at both Mercator and Prévimer are stakeholders in this project and the results will directly benefit their work.

The main objective of this project is to improve the implementation of open boundaries (Open Boundary Conditions: OBCs) in the coupled physical-biogeochemical models operated at regional scales.
The main focus is to understand how to manage and apply the biogeochemical forcing at the open boundaries (OBCs) in regional models if they originate from an external source (in particular a global scale model, a climatology, or in situ/spatial measurements) to obtain a better representation of the process at the interfaces, in particular the cross-shelf exchange processes between the continental shelf and the abyssal plain.

The project is divided into 2 main phases:

  • Phase 1: Testing one regional model (R1, R2, R3 or R4) with different forcings (external/internal) at the open boundaries
  • Phase 2 is divided into three stages:
    • testing one or more configurations with various OBC forcings
    • evaluation of model performance based on predefined metrics for each study area, with respect to the local currents (slope current in Bay of Biscay and Northern Current in the Gulf of Lion)
    • establish a protocol to force OBCs of Regional models