Surface Connectivity and Interocean Exchanges From Drifter‐Based Transition Matrices

Abstract

Global surface transport in the ocean can be represented by using the observed trajectories of drifters to calculate probability distribution functions. The oceanographic applications of the Markov Chain approach to modeling include tracking of floating debris and water masses, globally and on yearly‐to‐centennial time scales. Here we analyze the error inherent with mapping trajectories onto a grid and the consequences for ocean transport modeling and detection of accumulation structures. A sensitivity analysis of Markov Chain parameters is performed in an idealized Stommel gyre and western boundary current as well as with observed ocean drifters, complementing previous studies on widespread floating debris accumulation. Focusing on two key areas of interocean exchange—the Agulhas system and the North Atlantic intergyre transport barrier—we assess the capacity of the Markov Chain methodology to detect surface connectivity and dynamic transport barriers. Finally, we extend the methodology's functionality to separate the geostrophic and nongeostrophic contributions to interocean exchange in these key regions.

Role of Indian Ocean Dynamics on Accumulation of Buoyant Debris

“…More specifically, van Sebille et al () compared global particle tracking simulations forced by a hydrodynamic model by Lebreton et al () to drifter transport matrix simulations by Maximenko et al (). On the basin scale the results were similar and the drifter transport matrix method is therefore considered adequate to represent the large spatial and temporal scale transport (McAdam & van Sebille, ).…”

“…Depending on the position of the Argos or Global Positioning System satellites, drifter locations are accurate within 15‐m to 1‐km (Lumpkin & Pazos, ). These errors are negligible for transport between 1° grid cells (see section ) that we are interested in here (McAdam & van Sebille, ). The spatial coverage of the drifters spans most of the global oceans (Figure a).…”

“…These are important regions of exchange between oceans and the relative undersampling of these regions is a limitation of the drifter transport matrix method. However, the subtropical ocean basins contain between and drifter locations per 1° grid cells, which is sufficient to represent the dynamics of the subtropical accumulation regions that we are interested in (e.g., Cózar et al, ; Maximenko et al, ; McAdam & van Sebille, ; Sherman & van Sebille, ).…”

“…As a result, these effects are present in the observed drifter locations that we use to construct transport matrices, regardless of the grid cell size dx and separation time dt . However, the discretization into grid cells of finite size dx and a finite separation time dt can lead to artificial dispersion in the transport matrix (Maximenko et al, ; McAdam & van Sebille, ). The reasons for this are explained in detail by McAdam and van Sebille ().…”

Connectivity of Pulley Ridge With Remote Locations as Inferred From Satellite‐Tracked Drifter Trajectories

“…We do not model variation of the advection‐diffusion dynamics as a function of initial time. This statistical stationarity assumption, commonly made in turbulence studies (Orszag, ), has been considered in prior transfer operator analyses of drifter data (Maximenko et al, ; McAdam & van Sebillet, ; Miron et al, ). In particular, Miron et al () show that random reductions of the data set do not substantially affect the connectivity results.…”