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To mitigate temporal aliasing effects in monthly mean global gravity fields from the GRACE and GRACE‐FO satellite tandem missions, both tidal and non‐tidal background models describing high‐frequency mass variability in atmosphere and oceans are needed. To quantify tides in the atmosphere, we exploit the higher spatial (31 km) and temporal (1 hr) resolution provided by the latest atmospheric ECMWF reanalysis, ERA5. The oceanic response to atmospheric tides is subsequently modeled with the general ocean circulation model MPIOM (in a recently revised TP10L40 configuration that includes the feedback of self‐attraction and loading to the momentum equations and has an improved bathymetry around Antarctica) as well as the shallow water model TiME (employing a much higher spatial resolution and more elaborate tidal dissipation than MPIOM). Both ocean models consider jointly the effects of atmospheric pressure variations and surface wind stress. We present the characteristics of 16 waves beating at frequencies in the 1–6 cpd band and find that TiME typically outperforms the corresponding results from MPIOM and also FES2014b as measured from comparisons with tide gauge data. Moreover, we note improvements in GRACE‐FO laser ranging interferometer range‐acceleration pre‐fit residuals when employing the ocean tide solutions from TiME, in particular, for the S1 spectral line with most notable improvements around Australia, India, and the northern part of South America. Plain Language Summary: In addition to many rather slow processes such as the melting of glaciers, rapid mass redistribution related to the weather also measurably affect the Earth's gravity field. The ability of monitoring liquid freshwater changes within the Earth system from the satellite gravity missions GRACE (2002–2017) and GRACE‐FO (since 2018) relies on accurate background models of mass variability in atmosphere and oceans for both tidal and non‐tidal processes. Atmospheric tides are primarily excited in the middle atmosphere by solar energy absorption at periods of 24 hr and its overtones. We find additional tidal signatures in the atmosphere excited by periodic deformations of both crust and sea‐surface of the Earth. We thus introduce here a new data set for the atmospheric tides and their corresponding oceanic response that features both more waves and higher accuracy than other background models previously used for the processing of GRACE and GRACE‐FO satellite gravimetry data. Key Points: Sixteen relevant tidal lines identified in hourly data from ERA5 atmospheric reanalysisDedicated simulations with a high‐resolution global hydrodynamic model to simulate ocean tides with atmospheric influenceNew tidal models reduce pre‐fit residuals in GRACE‐FO Laser Ranging Interferometer data [ABSTRACT FROM AUTHOR]

Here we isolate groundwater responses to atmospheric forcing of surface water levels by relating anomalies in coastal aquifer hydraulic head time‐series to weather events. Our results demonstrate that atmospheric forcing has a greater effect on groundwater exchange and extended residence time over astronomical tidal pumping at times. During winter, atmospheric groundwater forcing was associated with winter storm passage and had a recurrence interval of approximately 7 days. During summer, atmospheric groundwater forcing was limited to weak diurnal atmospheric convection and infrequent tropical cyclone activity. Because winter storms and tropical cyclones commonly produce precipitation, atmospheric groundwater forcing can synergize with the timing of meteoric recharge producing periods of intense submarine groundwater discharge. Plain Language Summary: Groundwater discharges from the seafloor into coastal waters through a process known as submarine groundwater discharge. Submarine groundwater discharge is composed of fresh water from the land and recirculated seawater drawn into the seafloor by ocean processes. In this manuscript, we document the effect of shifting winds brought about by winter storms, tropical cyclones, and land/sea breezes on seawater recirculation through seafloor sediments. Strong onshore winds cause regional mounding of seawater against the shoreline and infiltration into coastal aquifers while offshore winds allow groundwater to drain from the seafloor back into coastal waters. This effect we term, atmospheric groundwater forcing, leads to periods of intense submarine groundwater discharge following tropical cyclones and winter storms. Key Points: Atmospheric groundwater forcing is a seawater recirculation process driven by wind forcing of coastal surface water levelsAtmospheric groundwater forcing is seasonally associated with winter storms, tropical cyclones, and atmospheric convection cyclesThe timing of atmospheric groundwater forcing can synergize with meteoric recharge leading to subterranean estuary flushing [ABSTRACT FROM AUTHOR]

The modern history of North Atlantic sea surface temperature shows variability coinciding with changes in air temperature and rainfall over the Northern Hemisphere. There is a debate about this variability and, in particular, whether it is internal to the ocean‐atmosphere system or is forced by external factors (natural and anthropogenic). Here we present a temperature record, obtained using the Sr/Ca ratio measured in a skeleton of a sclerosponge, that shows agreement with the instrumental record over the past 150 years as well as multidecadal temperature variability over the last 600 years. Comparison with climate simulations of the last millennium shows that large cooling events recorded, in the sclerosponge, are consistent with natural (primarily volcanic activity) and anthropogenic forcings. There are, however, multidecadal periods not connected to current estimates of external forcing over the last millennium allowing for alternative explanations, such as internally driven changes in ocean and atmospheric circulation. Key Points: A high‐resolution 600‐year proxy temperature record from the subtropical Atlantic shows multidecadal temperature variabilityIn both models and observations, surface temperatures at this site are reflective of basin‐wide multidecadal variabilityComparison with Last Millennium climate model simulations shows the fingerprint of volcanically induced cooling [ABSTRACT FROM AUTHOR]

Interannual variability of Ocean Heat Content (OHC) is intimately linked to ocean water mass changes. Water mass characteristics are imprinted at the ocean surface and are modulated by climate variability on interannual to decadal time scales. In this study, we investigate the water mass change and their variability using an isopycnal decomposition of the OHC. For that purpose, we address the thickness and temperature changes of these water masses using both individual temperature‐salinity profiles and optimal interpolated products from Argo data. Isopycnal decomposition allows us to characterize the water mass interannual variability and decadal trends of volume and OHC. During the last decade (2006–2015), much of interannual and decadal warming is associated with Southern Hemisphere Subtropical Mode Water and Subantarctic Mode Water, particularly in the South Pacific Eastern Subtropical Mode Water, the Southeastern Indian Subantarctic Mode Water, and the Southern Pacific Subantarctic Mode Water. In contrast, Antarctic Intermediate Water in the Southern Hemisphere and North Atlantic Subtropical Mode Water in the Northern Hemisphere have cooled. This OHC interannual variability is mainly explained by volume (or mass) changes of water masses related to the isopycnal heaving. The forcing mechanisms and interior dynamics of water masses are discussed in the context of the wind stress change and ocean adjustment occurring at interannual time scale. Key Points: Upper global ocean mode water are the hot spots of 2006–2015 ocean heat trendSouthern Hemisphere mode water gained volume and buoyancy over 2006–2015Wind forcing and oceanic adjustment may partly explain the interannual mode water volume change [ABSTRACT FROM AUTHOR]

The Hudson Bay Complex is the outlet for many Canadian rivers, receiving roughly 900 km3/year of river runoff. Historically, studies found a consistent cyclonic flow year‐round in Hudson Bay, due to the geostrophic boundary current induced by river discharge and cyclonic wind forcing that was supported by available observations at that time. Using a high‐resolution ocean general circulation model, we show that in summer, the mean circulation is not cyclonic but consists of multiple small cyclonic and anticyclonic features, with the mean flow directed through the center of the bay. Absolute Dynamic Topography and velocity observations also show this seasonal flow pattern. We find that this summer circulation is driven by geostrophic currents, generated by steric height gradients, which are induced by increased river discharge during the spring freshet, and reinforced by anticyclonic seasonal wind patterns. Plain Language Summary: Knowing the direction of the currents, as well as speed, in Hudson Bay is important for understanding regional ocean flow patterns. Currents in Hudson Bay were historically thought to flow counterclockwise. We use a state‐of‐the‐art computer simulation to see if this flow pattern changes during the year. We found that in May and June, the flow pattern in eastern Hudson Bay reverses and the currents flow in a clockwise direction, while currents in western Hudson Bay still flow counterclockwise. Satellite measurements of ocean currents also show this switch in the current direction in eastern Hudson Bay. This reversal of the current direction occurs because of a change in the wind direction as well as the amount of river water entering the bay during spring (May–June). In spring, river water flowing into the bay increases because of snow melt. More river water enters southeastern Hudson Bay, in and around James Bay, causing higher sea levels in the east compared to the west. This water will flow from high to low (east to west), causing the clockwise flow pattern in summer. Key Points: The spring freshet increases the halosteric height in eastern Hudson Bay, generating a seasonal flowThis anticyclonic seasonal flow pattern is present in observations and the ocean model simulationGeostrophic flow that is reinforced by atmospheric forcing drives this springtime flow pattern [ABSTRACT FROM AUTHOR]

Abstract: Atlantic Water (AW) transported from the Nordic Seas is the major source of oceanic heat to the Arctic Ocean. Based on results from the TOPAZ reanalysis, a regional coupled ice‐ocean data assimilation system, we show that interannual variability of AW temperature in the Fram Strait (FS) is associated with the strength of the Greenland Sea gyre (GSG) circulation. The response of the GSG to the anomalous wind stress curl over the Nordic Seas modifies the AW inflow and thus influences the variability of AW temperature in the FS. A stronger (weaker) GSG circulation increases (decreases) the AW flow speed toward FS, leading to increased (decreased) oceanic heat content and higher (lower) AW temperature therein. This implies that the Nordic Seas circulation is not only a passive conduit of AW, but its response to overlying atmospheric variability can also largely influence the AW temperature in the FS by modifying the transport of AW. [ABSTRACT FROM AUTHOR]

The Community Climate System Model, version 4 ( CCSM4) is evaluated against reanalysis data for the late-twentieth century (1955-2005), with a focus on the ecologically and commercially important Bering Sea in the subarctic Pacific. Several atmospheric variables including surface-air temperature, sea level pressure, wind strength, and direction were evaluated due to their relevance to large marine ecosystems. Simulated spatial patterns of climatological surface-air temperature over the Bering Sea are generally well simulated despite some subregional biases as large as +3 °C during autumn and −5 °C during winter. Interannual variability of simulated surface-air temperature exceeds that of the reanalysis by a factor of nearly 1.5. Model simulations show an under-simulated Siberian high and a large northwest displacement of the Aleutian Low-pressure centre. Further, sea level pressure over the Bering Sea is under-simulated in winter and fall by more than 8 hPa, and over-simulated in summer by more than 5 hPa. Interannual variability in simulated sea level pressure is nearly twice as large as observed. In general, the CCSM4 shows an improved representation of both monthly mean surface-air temperature and sea level pressure over the subarctic Pacific relative to its predecessor, the CCSM3. Despite these advances, there is still a clear need for improvements in the model's representation of high-latitude atmospheric circulation in order to achieve proper atmospheric forcing of marine ecosystem models. [ABSTRACT FROM AUTHOR]

Despite the availability of several atmospheric reanalyses (e.g. ERA-Interim) there exists both considerable uncertainty in surface forcing fields for ice/ocean modelling and sensitivity to the choice of product used. Here we introduce a relatively high-resolution alternative forcing dataset for ice-ocean models derived from the Canadian Meteorological Centre's (CMC) global deterministic prediction system (GDPS). A set of daily 30 h reforecasts is produced using the GDPS 33 km resolution model providing hourly atmospheric forcing fields for the period 2002-2011. The CMC GDPS reforecasts (CGRF) are compared with ERA-Interim and several observational datasets to evaluate their suitability for forcing ocean models. In particular, the surface temperature, humidity and winds of the CGRF show equivalent biases to those found in ERA-interim. Moreover, the higher resolution of the CGRF permit a more detailed representation of atmospheric structures and topographic steering, resulting in finer-scale coastal features and wind-stress curl. Although the CGRF dataset is not a reanalysis and thus is expected to be less well constrained by available observations, its higher resolution and small bias make it an attractive alternative for forcing ice-ocean models. [ABSTRACT FROM AUTHOR]

The investigation of larval dispersal and retention, their variability and dependence on wind conditions, has become a major topic in fisheries research owing to potential effects on stock recruitment and stock structuring. The present study quantifies the wind-induced variability of larval retention of herring in a highly productive coastal lagoon of the Western Baltic Sea. This lagoon, the Greifswalder Bodden, represents the main spawning area of Western Baltic Spring-Spawning Herring, a stock that has recently undergone a continuous decline in recruitment. The study tests whether this decline was related to changes in larval retention, more precisely to changes in wind conditions, the main forcing of the lagoon's circulation. To answer this, a model approach was applied. Larvae were tracked as Lagrangian drifters under constant and variable wind conditions, examining the main drift patterns and reconstructing the incidents during the period of recruitment decline. For the latter, weekly cohorts of virtual larvae were released in the lagoon over the entire spawning period (April-June; >16 weeks). The fraction of retained larvae per cohort was related to observed larval abundances. On this basis, a new retention index was defined to evaluate the annual larval retention. The results presented cannot explain the observed recruitment decline but characterize the lagoon as an important larval retention area by virtue of unsteady wind conditions that prevent a steady outflow of larvae. [ABSTRACT FROM AUTHOR]

The article presents a study on the winter-mean sea surface temperature's (SST) long-term variability in Black and Aegean Seas and its correlation with several atmospheric forcing. It states that satellite and reanalysis data from 1982 to 2004 were used examine the correlation with the atmospheric forcing which include surface air temperature (SAT). Results show that SST variability is correlated with the SAT variability while SAT is correlated with the meridional component of the surface wind.

Abstract A three-dimensional hydrodynamic model has been used to analyse temporally and spatially resolved circulation patterns in the Baltic Sea with special emphasis on drifting particles representing larval fish. The main purpose of this study was (i) to investigate potential drift patterns of larval fish, (ii) to identify its intra- and inter-annual variability for time periods based on the timing of spawning and (iii) to analyse its seasonal and spatial variability in dependence of the atmospheric forcing conditions. For the time period 1979–1998 temporally and spatially resolved simulated flow fields were used to describe the potential drift from the centre of main reproductive effort of Baltic cod (Gadus morhua ). The results of the model runs demonstrate a general change in circulation pattern from retention during a first decade (1979–1988) to dispersion in the following decade (1989–1998). This increase in dispersion was related to an increase in the variability of the local wind forcing conditions over the Baltic. The more frequent occurrence of dispersion in spring of the recent decade was accompanied by a strong decay in biomass of one of the main larval fish feeding component in the central basin, the calanoid copepod Pseudocalanus elongatus . Larger dispersion of this prey organism may have affected the spatial overlap and thus the contact rates between predator and prey. Hence, this may have resulted in a food limitation for early life stages of Baltic cod and potentially contributed to the pronounced shift in cod peak spawning time from spring to late summer. Early life stages of cod originating from late spawning fish, benefited from a stronger dispersion in late summer and autumn, into shallow coastal areas with higher calanoid abundance. [ABSTRACT FROM AUTHOR]

Abstract Oceanic inflow is estimated to contribute more than 90% of the nutrient input into the North Sea. Variability in the volume, chemical properties, biological content and source of the inflowing water is thus likely to have a considerable effect on North Sea ecosystems. Changes seen in the plankton, and in particular Calanus finmarchicus and Calanus helgolandicus , over the last 40 years as measured by the Continuous Plankton Recorder survey, allow clear periods to be identified that appear to be associated with variability in inflow. Monthly estimates of inflow and outflow across a section between Orkney and Utsira in Norway as well as netflow (sum of Baltic outflow, runoff and Channel inflow), have been derived from runs of the NORWECOM model for two integrated depth intervals: surface to 150 m and >150 m. A comparison is made between the physical model output and plankton results for the period 1958–99. Distinct plankton periods that appear to reflect changing inflow events are discussed in relation to hydrometeorological and earlier plankton studies over approximately the last 100 years. [ABSTRACT FROM AUTHOR]

A global ¼° ocean/sea‐ice 50‐member ensemble simulation is analyzed to disentangle the imprints of the atmospheric forcing and the chaotic ocean variability on regional sea level trends over the satellite altimetry period. We find that the chaotic ocean variability may mask atmospherically forced regional sea level trends over 38% of the global ocean area from 1993 to 2015, and over 47% of this area from 2005 to 2015. These regions are located in the western boundary currents, in the Southern Ocean and in the subtropical gyres. While these results do not question the anthropogenic origin of global mean sea level rise, they give new insights into the intrinsically oceanic versus atmospheric forcing of regional sea level trends and provide new constraints on the measurement time required to attribute regional sea level trends to the atmospheric forcing or to climate change. Plain Language Summary: As a direct consequence of anthropogenic influences, global mean sea level rises in response to ocean warming and land ice melting. Since the early 1990s, satellite altimetry has revealed large regional contrasts in sea level trends, controlled by temperature and salinity changes, oceanic processes and atmospheric forcing. Using an ensemble of forced eddying ocean simulations, we show that regional sea level trends over the altimetric period are only partly determined by the atmospheric evolution (both natural and anthropogenic): nonlinear ocean processes produce additional sea level trends that are inherently random, which can compete in certain regions with the externally forced trends. These results do not question the existence of global and regional sea level trends, but suggest that sea level trends may not be unambiguously attributed to external causes in certain regions. Key Points: Atmospheric drivers force regional sea level trends over most of the global ocean area since 1993Chaotic ocean variability may mask these atmospherically forced regional trends over a substantial fraction of the global ocean areaIn the latter regions, altimeter‐derived regional sea level trends may not be representative of anthropogenic or atmospheric causes [ABSTRACT FROM AUTHOR]