Abstract
Abstract. Past characterizations of the land–ocean continuum were constructed either from a continental perspective through an analysis of watershed river basin properties (COSCATs: COastal Segmentation and related CATchments) or from an oceanic perspective, through a regionalization of the proximal and distal continental margins (LMEs: large marine ecosystems). Here, we present a global-scale coastal segmentation, composed of three consistent levels, that includes the whole aquatic continuum with its riverine, estuarine and shelf sea components. Our work delineates comprehensive ensembles by harmonizing previous segmentations and typologies in order to retain the most important physical characteristics of both the land and shelf areas. The proposed multi-scale segmentation results in a distribution of global exorheic watersheds, estuaries and continental shelf seas among 45 major zones (MARCATS: MARgins and CATchments Segmentation) and 149 sub-units (COSCATs). Geographic and hydrologic parameters such as the surface area, volume and freshwater residence time are calculated for each coastal unit as well as different hypsometric profiles. Our analysis provides detailed insights into the distributions of coastal and continental shelf areas and how they connect with incoming riverine fluxes. The segmentation is also used to re-evaluate the global estuarine CO2 flux at the air–water interface combining global and regional average emission rates derived from local studies.
Highlights
The land–ocean aquatic continuum is commonly defined as the interface, or transition zone, between terrestrial ecosystems and the open ocean (Billen et al, 1991; Mackenzie et al, 2012; Rabouille et al, 2001; Regnier et al, 2013)
The land– ocean aquatic continuum is acknowledged to play a significant role in global biogeochemical cycles (Gattuso et al, 1998; Mackenzie et al, 1998; Mantoura et al, 1991), the quantitative contribution of inland waters, estuaries and continental shelves to carbon and nutrient budgets remains entailed with large uncertainties, reflecting primarily the limited availability of field data and the lack of robust upscaling approaches (Regnier et al, 2013)
The colour code corresponds to the MARCATS classification, the continental shelves being highlighted in slightly darker colours
Summary
The land–ocean aquatic continuum is commonly defined as the interface, or transition zone, between terrestrial ecosystems and the open ocean (Billen et al, 1991; Mackenzie et al, 2012; Rabouille et al, 2001; Regnier et al, 2013). We present a harmonized multi-scale segmentation for the land–ocean continuum, from the watershed to the outer limit of the continental shelf It is based on three increasing levels of aggregation, and the inter-compatibility of these levels allows the integration of a wide variety of databases compiled at various spatial resolutions, and the comparison and combination of them with one another. The highest level in the hierarchy is termed MARCATS (for MARgins and CATchments Segmentation) and consists of aggregated COSCAT units according to the main climatological, morphological and oceanographic characteristics of the coastal zone This new segmentation is inspired by a classification of the continental shelf seas proposed in the recent synthesis by Liu et al (2010) and defines 45 regional units, which allow for coarser regional analysis and upscaling calculations when data sets are limited. The GIS files provided in the Supplement will allow the community to alter the approach or to refine local settings if needed
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