On Using Lagrangian Drift Simulations to Aid Interpretation of in situ Monitoring Data

Abstract

One key challenge of marine monitoring programs is to reasonably combine information from different in situ observations spread in space and time. In that context, we suggest the use of Lagrangian transport simulations extending both forward and backward in time to identify the movements of water bodies from the time they were observed to the time of their synopsis. We present examples of how synoptic maps of salinity generated by this method support the identification and tracing of river plumes in coastal regions. We also demonstrate how we can use synoptic maps to delineate different water masses in coastal margins. These examples involve quasi-continuous observations of salinity taken along ferry routes. A third application is the synchronization of measurements between fixed stations and nearby moving platforms. Both observational platforms often see the same water body, but at different times. We demonstrate how the measurements from a fixed platform can be synchronized to measurements from a moving platform by taking into account simulation-based time shifts.

Dissolved trace elements and nutrients in the North Sea—a current baseline

“…For the surface sample near Arendal, the salinity was lower (30 psu) than the deeper and surrounding samples (33–35 psu), indicating that this water mass might have originated from the Kattegat (Aure et al, 1998 ; Kristiansen & Aas, 2015 ). This is supported by a surface drift model 1 (Callies et al, 2021 ) showing that the water mass originated from the eastern Skagerrak during HE586, while the currents were different during AL557 (Fig. S40 ).…”

“…In contrast, for AL557 st.4, the surface drift model 1 (Fig. S39 ; Callies et al, 2021 ) showed that the water mass has been moving in the region due to tidal activity but might have originated from the Eider or Elbe estuary. This would be supported by the low salinity of this sample (Fig.…”

“…S12 ). These likely originated from the German Bight, as a surface water drift model 1 (Callies et al, 2021 ) indicated the northward transport of these water masses via the southern Jutland current (Fig. S39 ).…”

Data Analysis and Exploration with Computational Approaches

“…The data are made available in near real time via the COSYNA (Coastal Observing System for Northern and Arctic Seas) data portal (Baschek et al 2017;Breitbach et al 2016). The PELETS-2D code (Callies et al 2021) is used to compute model trajectories for each FerryBox transect. These model trajectories consist of the measured water bodies' positions up to ten days before and after the actual measurement as simulated by the numeric model.…”