The tilt of mean sea level along the east coast of North America

The tilt of mean sea level along the North American east coast has been a subject of debate for many decades. Improvements in geoid and ocean circulation models, and GPS positioning of tide gauge benchmarks, provide an opportunity to produce new tilt estimates. Tilts estimated using tide gauge measurements referenced to high-resolution geoid models (the geodetic approach) and ocean circulation models (the ocean approach) are compared. The geodetic estimates are broadly similar, with tilts downward to the north through the Florida Straits and at Cape Hatteras. Estimates from the ocean approach show good agreement with the geodetic estimates, indicating a convergence of the two approaches and resolving the long standing debate as to the sign of the tilt. These tilts differ from those used by Yin and Goddard (2013) to support a link between changing ocean circulation and coastal sea level rise

Improved Internal Wave Spectral Continuum in a Regional Ocean Model

Recent work demonstrates that high‐resolution global models forced simultaneously by atmospheric fields and the astronomical tidal potential contain a partial internal (gravity) wave (IW) spectral continuum. Regional simulations of the MITgcm forced at the horizontal boundaries by a global run that carries a partial IW continuum spectrum are performed at the same grid spacing as the global run and at finer grid spacings in an attempt to fill out more of the IW spectral continuum. Decreasing only the horizontal grid spacing from 2 to 0.25 km greatly improves the frequency spectra and slightly improves the vertical wavenumber spectra of the horizontal velocity. Decreasing only the vertical grid spacing by a factor of 3 does not yield any significant improvements. Decreasing both horizontal and vertical grid spacings yields the greatest degree of improvement, filling the frequency spectrum out to 72 cpd. Our results suggest that improved IW spectra in regional models are possible if they are run at finer grid spacings and are forced at their lateral boundaries by remotely generated IWs. Additionally, consistency relations demonstrate that improvements in the spectra are indeed due to the existence of IWs at higher frequencies and vertical wavenumbers when remote IW forcing is included and model grid spacings decrease. By being able to simulate an IW spectral continuum to 0.25 km scales, these simulations demonstrate that one may be able to track the energy pathways of IWs from generation to dissipation and improve the understanding of processes such as IW‐driven mixing.Plain Language SummaryModels of internal waves (IWs) may help us to better understand the spatial geography of mixing in the ocean and are playing an increasingly important role in the planning of satellite missions. Following recent work showing that high‐resolution global models contain a partial IW spectrum, this paper describes further improvements in the spectrum seen in a high‐resolution regional model forced at the boundaries by a previously performed global IW simulation. Decreasing only the horizontal grid spacing greatly improves the frequency spectra and slightly improves the vertical wavenumber spectra of velocity. Increasing only the number of vertical levels does not yield any significant improvements. Decreasing both horizontal and vertical grid spacings yields the greatest improvement in both spectra. Our results suggest that regional models can exhibit improved IW spectra over global models if two conditions are met—they must have higher horizontal and vertical resolutions, and they must have remotely generated IWs at their boundaries. Application of the so‐called consistency relations demonstrates that the model is indeed carrying a field of high‐frequency IWs. Being able to simulate a fuller IW spectrum demonstrates that one may be able to use these models to improve the understanding of IW‐driven processes and energy pathways.Key PointsInternal gravity wave spectra in regional models are more realistic as model grid spacing decreasesThe vertical wavenumber spectra improve less dramatically than the frequency spectraInternal gravity wave consistency relations are applied to modeled spectraPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154917/1/jgrc23947_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154917/2/jgrc23947.pd

Inferring connectivity range in submerged aquatic populations (<i>Ruppia</i> L.) along European coastal lagoons from genetic imprint and simulated dispersal trajectories

Coastal salt- and brackish water lagoons are unique shallow habitats characterized by beds of submerged seagrasses and salt-tolerant Ruppia species. Established long-term and large-scale patterns of connectivity in lagoon systems can be strongly determined by patterns of nearshore and coastal currents next to local bird-mediated seed dispersal. Despite the importance of dispersal in landscape ecology, characterizing patterns of connectivity remains challenging in aquatic systems. Here, we aimed at inferring connectivity distances of Ruppia cirrhosa along European coastal lagoons using a population genetic imprint and modeled dispersal trajectories using an eddy-resolving numerical ocean model that includes tidal forcing. We investigated 1,303 individuals of 46 populations alongside subbasins of the Mediterranean (Balearic, Tyrrhenian, Ionian) and the Atlantic to Baltic Sea coastline over maximum distances of 563–2,684 km. Ten microsatellite loci under an autotetraploid condition revealed a mixed sexual and vegetative reproduction mode. A pairwise FST permutation test of populations revealed high levels of historical connectivity only for distance classes up to 104–280 km. Since full range analysis was not fully explanatory, we assessed connectivity in more detail at coastline and subbasin level using four approaches. Firstly, a regression over restricted geographical distances (300 km) was done though remained comparable to full range analysis. Secondly, piecewise linear regression analyses yielded much better explained variance but the obtained breakpoints were shifted toward greater geographical distances due to a flat slope of regression lines that most likely reflect genetic drift. Thirdly, classification and regression tree analyses revealed threshold values of 47–179 km. Finally, simulated ocean surface dispersal trajectories for propagules with floating periods of 1–4 weeks, were congruent with inferred distances, a spatial Bayesian admixed gene pool clustering and a barrier detection method. A kinship based spatial autocorrelation showed a contemporary within-lagoon connectivity up to 20 km. Our findings indicate that strong differentiation or admixtures shaped historical connectivity and that a pre- and post LGM genetic imprint of R. cirrhosa along the European coasts was maintained from their occurrence in primary habitats. Additionally, this study demonstrates the importance of unraveling thresholds of genetic breaks in combination with ocean dispersal modeling to infer patterns of connectivity

A Rossby whistle: a resonant basin mode observed in the Caribbean Sea

We show that an important source of coastal sea level variability around the Caribbean Sea is a resonant basin mode. The mode consists of a baroclinic Rossby wave which propagates westward across the basin and is rapidly returned to the east along the southern boundary as coastal shelf waves. Almost two wavelengths of the Rossby wave fit across the basin, and it has a period of 120 days. The porous boundary of the Caribbean Sea results in this mode exciting a mass exchange with the wider ocean, leading to a dominant mode of bottom pressure variability which is almost uniform over the Grenada, Venezuela, and Colombia basins and has a sharp spectral peak at 120 day period. As the Rossby waves have been shown to be excited by instability of the Caribbean Current, this resonant mode is dynamically equivalent to the operation of a whistle

On the Effects of Increased Vertical Mixing on the Arctic Ocean and Sea Ice

Against the backdrop of Arctic sea ice decline, vertical mixing in the interior Arctic Ocean will most likely change, but it is still unclear how the Arctic Ocean and sea ice will respond. In this paper, a sea ice‐ocean model with a simple parameterization for interior background mixing is used to investigate the Arctic Ocean and sea ice response to a scenario of increased vertical mixing. It is found that more vertical mixing reduces sea ice thickness all year round and decreases summertime sea ice concentration. More vertical mixing leads to a cooling of the Arctic halocline layer and Atlantic Water layer below. The increased vertical mixing speeds up vertical heat and salinity exchange, brings the underlying warm and saline water into the surface layer, and contributes to the sea ice decline. Vertical salinity gradient of the Arctic halocline layer reduces together with a much fresher Atlantic Water layer, and more volume of saline water enters the deep ocean below the Atlantic Water layer. As a result, the reduced Arctic Ocean stratification leads to an adjustment of the circulation pattern. Cyclonic circulation anomalies occur in the surface layer shallower than 20m depth and in the interior ocean deeper than 700m depth, while anticyclonic circulation anomalies occur between these depths. Our study suggests that the extra heat and salinity exchange induced by more vertical mixing will have a noticeable impact on the upper ocean structure, ocean circulation, and sea ice in a changing Arctic Ocean

Attribution of space-time variability in global-ocean dissolved inorganic Carbon

The inventory and variability of oceanic dissolved inorganic carbon (DIC) is driven by the interplay of physical, chemical, and biological processes. Quantifying the spatiotemporal variability of these drivers is crucial for a mechanistic understanding of the ocean carbon sink and its future trajectory. Here, we use the Estimating the Circulation and Climate of the Ocean-Darwin ocean biogeochemistry state estimate to generate a global-ocean, data-constrained DIC budget and investigate how spatial and seasonal-to-interannual variability in three-dimensional circulation, air-sea CO2 flux, and biological processes have modulated the ocean sink for 1995–2018. Our results demonstrate substantial compensation between budget terms, resulting in distinct upper-ocean carbon regimes. For example, boundary current regions have strong contributions from vertical diffusion while equatorial regions exhibit compensation between upwelling and biological processes. When integrated across the full ocean depth, the 24-year DIC mass increase of 64 Pg C (2.7 Pg C year−1) primarily tracks the anthropogenic CO2 growth rate, with biological processes providing a small contribution of 2 (1.4 Pg C). In the upper 100 m, which stores roughly 13 (8.1 Pg C) of the global increase, we find that circulation provides the largest DIC gain (6.3 Pg C year−1) and biological processes are the largest loss (8.6 Pg C year−1). Interannual variability is dominated by vertical advection in equatorial regions, with the 1997–1998 El Niño-Southern Oscillation causing the largest year-to-year change in upper-ocean DIC (2.1 Pg C). Our results provide a novel, data-constrained framework for an improved mechanistic understanding of natural and anthropogenic perturbations to the ocean sink. © 2022. The Authors