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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.

Measurements of near-surface oxygen (O2) concentrations and mixed layer depth from the K1 mooring in the central Labrador Sea are used to calculate the change in column-integrated (0–1700 m) O2 content over the deep convection winter 2014/2015. During the mixed layer deepening period, November 2014 to April 2015, the oxygen content increased by 24.3 ± 3.4 mol m−2, 40% higher than previous results from winters with weaker convection. By estimating the contribution of respiration and lateral transport on the oxygen budget, the cumulative air-sea gas exchange is derived. The O2 uptake of 29.1 ± 3.8 mol m−2, driven by persistent undersaturation (≥5%) and strong atmospheric forcing, is substantially higher than predicted by standard (nonbubble) gas exchange parameterizations, whereas most bubble-resolving parameterizations predict higher uptake, comparable to our results. Generally large but varying mixed layer depths and strong heat and momentum fluxes make the Labrador Sea an ideal test bed for process studies aimed at improving gas exchange parameterizations.

The 2015-2016 El Nino contributed to large anomalies across the California Current System (CalCS), but these anomalies ceased unexpectedly in late 2015. Here, we use a suite of three hindcast simulations with the Regional Oceanic Modeling System (ROMS) to assess the responsible mechanisms for this development. We find that the early build-up was primarily driven by the early onset of this event in the tropical Pacific, driving anomalies in the CalCS through the propagation of coastally trapped waves. In contrast, the abrupt end in the central CalCS was caused by the unusual onset of upwelling favorable winds in the fall of 2015, which offset the continuing remote forcing through the coastal waveguide. Nevertheless, low nutrient anomalies persisted, causing anomalously low phytoplankton abundance in the upwelling season of 2016. This is a recurring pattern for all El Nino events over the last 37 years, suggesting predictive skill on seasonal timescales.

Deep convection is presumed to be vital for the North Atlantic Meridional Overturning Circulation,even though observational evidence for the link remains inconclusive. Modeling studies have suggested thatconvection will weaken as a result of enhanced freshwater input. The emergence of anomalously low seasurface temperature in the subpolar North Atlantic has led to speculation that this process is already at work.Hereweshow that strong atmospheric forcing in the winter of 2014–2015, associated with a high North AtlanticOscillation (NAO) index, produced record mixed layer depths in the Irminger Sea. Local mixing removed thestratification of the upper 1400mand ventilated the basin to middepths resembling a state similar to themid-1990s when a positive NAO also prevailed. We show that the strong local atmospheric forcing ispredominantly responsible for the negative sea surface temperature anomalies observed in the subpolar NorthAtlantic in 2015 and that there is no evidence of permanently weakened deep convection.

Large-scale patterns of positive temperature anomalies persisted throughout the surface waters of the North Pacific Ocean during 2014–2015. In the Southern California Current System, measurements by our sustained network of underwater gliders reveal the coastal effects of the recent warming. Regional upper ocean temperature anomalies were greatest since the initiation of the glider network in 2006. Additional observed physical anomalies included a depressed thermocline, high stratification, and freshening; induced biological consequences included changes in the vertical distribution of chlorophyll fluorescence. Contemporaneous surface heat flux and wind strength perturbations suggest that local anomalous atmospheric forcing caused the unusual oceanic conditions.

The response of the oceanic circulation to mesoscale atmospheric forcing is studied by comparing integrations of a global sea ice-ocean model with high-resolution European Centre for Medium-Range Weather Forecasts analysis data (0.4◦) to those with the same forcing coarse grained to a resolution typically employed in climate models and atmospheric reanalyses (1.8◦). It is shown that the representation of mesoscale features in atmospheric forcing fields leads to an increase in the strength of the wind-driven gyres in the North Atlantic and North Pacific regions of about 5–10% of its mean value. An increase of similar magnitude is found for the Atlantic meridional overturning circulation. From the results of this study it is argued that small-scale atmospheric phenomena such as fronts, mesoscale cyclones, and topographic jets play an important role in driving the mean oceanic circulation.

[1] Hurricane Sandy drove storm surges throughout the eastern seaboard of the United States, from Miami to Maine, at the end of October 2012. The surge was particularly high (>3 m) in coastal New York. In the southeastern United States, the surge was

[1] The relative importance of tropical versus extratropical forcing on the southern annular mode (SAM) during the austral summer is explored using dry atmospheric model experiments with prescribed atmospheric forcing. The tropical forcing regions are determined based on areas of high observed correlations between atmospheric heating and the SAM. Diagnosed atmospheric forcing over the tropical America-Atlantic is found to be the major tropical driver of the SAM trend and interannual variability. Synoptic eddies tend to reinforce and maintain the SAM-associated circulation anomaly. Contribution of the tropical diagnosed forcing, as a whole, to the SAM trend over 1951–2010 is about one third in strength compared to that of the southern extratropical forcing processes.

[1] Variations in large-scale atmospheric forcing influence upwelling dynamics and ecosystem productivity in the California Current System (CCS). In this paper, we characterize interannual variability of the North Pacific High over 40 years and investigate how variation in its amplitude and position affect upwelling and biology. We develop a winter upwelling “pre-conditioning” index and demonstrate its utility to understanding biological processes. Variation in the winter NPH can be well described by its areal extent and maximum pressure, which in turn is predictive of winter upwelling. Our winter pre-conditioning index explained 64% of the variation in biological responses (fish and seabirds). Understanding characteristics of the NPH in winter is therefore critical to predicting biological responses in the CCS.

This study investigates the relationship between decadal changes in solar activity and sea level extremes along the European coasts and derived from tide gauge data. Autumn sea level extremes vary with the 11 year solar cycle at Venice as suggested by previous studies, but a similar link is also found at Trieste. In addition, a solar signal in winter sea level extremes is also found at Venice, Trieste, Marseille, Ceuta, Brest, and Newlyn. The influence of the solar cycle is also evident in the sea level extremes derived from a barotropic model with spatial patterns that are consistent with the correlations obtained at the tide gauges. This agreement indicates that the link to the solar cycle is through modulation of the atmospheric forcing. The only atmospheric regional pattern that showed variability at the 11 year period was the East Atlantic pattern.

[1] Hydrographic observations indicated a shift of the main deep water formation in the Mediterranean Sea from its usual location in the Adriatic Sea to the Aegean Sea during the late 1980s and early 1990s, during winters 1991/1992 and 1992/1993. This event is known as the Eastern Mediterranean Transient (EMT). We report here a connection between EMT and specific atmospheric conditions which created anomalously large buoyancy fluxes from the Aegean Sea during winters 1991/1992 and 1992/1993 (the “enhanced EMT winters”). We use newly available, state of the art datasets with high space and time resolution and show that atypical cyclonic activity in the central Mediterranean versus the eastern basin produced the enhanced atmospheric forcing which intensified the EMT. An abatement of the frequency of cyclones in the central Mediterranean during 1992/1993 drastically reduced the northward advection of warm air over the Aegean Sea compared to more typical years, while an increase in the frequency of cyclones in the eastern Mediterranean enhanced the southward advection of cold air over the Aegean Sea, especially during 1991/1992. These changes significantly increased buoyancy flux losses from the Aegean Sea during the enhanced EMT winters, intensifying deep water production.

[1] Pairs of moorings containing acoustic Doppler current profilers (ADCPs) were deployed at each end of the Bosphorus Strait as a part of the United States Naval Research Laboratory's “Exchange Processes in Ocean Straits (EPOS)” project. The moorings were deployed in September 2008 and remained in place for about half a year. For the first time, current velocity profiles were collected concurrently at both ends of the strait. They well resolved the two-layer exchange flow and were used to estimate volume flux time series. These estimates clearly indicated that there was a mean net volume flux of over 100 km3/yr directed from the Black Sea to the Sea of Marmara over this period. The upper-layer fluxes showed distinct temporal variability whereas the lower-layer fluxes varied less. Volume fluxes were maximized at over 1500 km3/yr in the upper layer and over 1100 km3/yr in the lower layer, with an upper-layer mean of about 400 km3/yr and a lower-layer mean of about 300 km3/yr. Fluxes in both layers were highly coherent with the bottom pressure difference between the southern and northern ends of Bosphorus Strait, and they can be fairly well predicted from this pressure difference. The fluxes in the upper layer were also influenced by atmospheric forcing, but generally less so than by the bottom pressure difference.

[1] The 2009–2010 El Nino marked the first occurrence of this climate phenomenon since the initiation of sustained autonomous glider surveillance in the California Current System (CCS). Spray glider observations reveal the subsurface effects of El Nino in the CCS with spatial and temporal resolutions that could not have been obtained practically with any other observational method. Glider observations show that upper ocean waters in the CCS were unusually warm and isopycnals were abnormally deep during the El Nino event, but indicate no anomalous water masses in the region. Observed oceanic anomalies in the CCS are nearly in phase with an equatorial El Nino index and local anomalies of atmospheric forcing. These observations point toward an atmospheric teleconnection as an important mechanism for the 2009–2010 El Nino's remote effect on the midlatitude CCS.

[1] The extent and strength of the North Atlantic subpolar gyre (SPG) changed rapidly in the mid-1990s, going from large and strong in 1995 to substantially weakened in the following years. The abrupt change in the intensity of the SPG is commonly linked to the reversal of the North Atlantic Oscillation (NAO) index, changing from strong positive to negative values, in the winter 1995/96. In this study we investigate the impact of the initial SPG state on the subsequent behavior of the SPG by means of an ocean general circulation model driven by NCEP-NCAR reanalysis fields. Our sensitivity integrations suggest that the weakening of the SPG cannot be explained by the change in the atmospheric forcing alone. Rather, for the time period around 1995, the SPG was about to weaken, irrespective of the actual atmospheric forcing, due to the ocean state governed by the persistently strong positive NAO during the preceding seven years (1989–1995). Our analysis indicates that it was this preconditioning of the ocean, in combination with the sudden drop in the NAO in 1995/96, that lead to the strong and rapid weakening of the SPG in the second half of the 1990s. This hypothesis explains the diverging evolution of the strength of the SPG and the atmospheric forcing (winter NAO) after 1995, as has been suggested recently.

The coherence between single bottom pressure .4 barotropic velocity records collected in the North c during BEMand air pressure, wind stress, and wind stress cuff derived from FNOC products are examined ovthe 2-'00-1 day period band. Strong coherence between the bottom pressure and all atmospheric variables is seen, with nonlocal coherence (maximum up to 1000 km to the southeast) dominating at periods longer than =!0 d and local coherence being prevalent at shorter periods, con- sistent with predictions from existing models of mospherically-forced barotropic motion. The azimuth of be .nonlocal coherence maximum relative to the ocean sta- firm is a function of frequency, which is not expected from the models. The coherence between the barotropic velocity (as measured by the electric field) and the atmospheric vari- ables is weaker, but nonlocal coherence with the wind stress and wind stress curl at periods greater than a week, .aM local coherence with the wind stress at shorter periods, is statis.cally significant.

[1] We compare daily data from the National Center for Atmospheric Research and National Centers for Environmental Prediction “Reanalysis 1” project with observational data obtained from the North Pole drifting stations in order to validate the atmospheric forcing data used in coupled ice-ocean models. This analysis is conducted to assess the role of errors associated with model forcing before performing model verifications against observed ocean variables. Our analysis shows an excellent agreement between observed and reanalysis sea level pressures and a relatively good correlation between observed and reanalysis surface winds. The observed temperature is in good agreement with reanalysis data only in winter. Specific air humidity and cloudiness are not reproduced well by reanalysis and are not recommended for model forcing. An example sensitivity study demonstrates that the equilibrium ice thickness obtained using NP forcing is two times thicker than using reanalysis forcing.

[1] A regional ocean model is applied to the tropical South East Atlantic Ocean in order to investigate the sensitivity of the intensity and position of the Angola Benguela Frontal Zone. The results suggest that the position of the Angola Benguela Frontal Zone is mainly determined by opposing northward and southward flow within 2 degrees off the coast. The windstress curl plays a major role in altering the position of the Angola Benguela Frontal Zone, as it controls the southeastward flow of the South Equatorial Counter Current. The opposing northward flow is mainly the result of geostrophic adjustment to coastal upwelling driven by the meridional windstress. The strength of the frontal zone is found to be related to the strength of the southerly windstress that controls the coastal upwelling.

Lower Circumpolar Deep Water (LCDW) is an important component of the global overturning circulation as it upwells south of the Antarctic Circumpolar Current (ACC) renewing the ocean interior. The LCDW also aids the transport of water properties between the major ocean basins. The property variability of the LCDW Salinity Maximum layer was examined using 37 meridional sections across Drake Passage between 1926–2004. Within the limits of experimental error and high frequency variability, the core properties of this layer have remained constant between 1926–2004. A comparison of modern sections and the 1932 Discovery II cruise indicates that this observation may be true for LCDW throughout the Southern Ocean. The significance of this result in terms of the observations of decadal changes in the Southern Ocean Intermediate and Mode waters is that these changes are most likely due to contemporary atmospheric forcing and not due to variations in the source water properties.

Extensive, collocated measurements of the mass concentrations of composite and black carbon (BC) aerosols were made over coastal Arabian Sea, adjoining Indian Peninsula, for the first time during the inter-monsoon and summer monsoon periods, of 2003, as part of Arabian Sea Monsoon Experiment (ARMEX). Results showed that the diurnal variations are weak in March, and vanish completely by May/June, associated with the change in the synoptic circulations. The concentration of BC (and its share to total aerosol mass) decreases continuously, from similar to700 ng m(-3) (2.5%) in March to similar to104 ng m(-3) (0.5%) by June. Consequently, the net atmospheric forcing (heating) efficiency decreases from similar to70 W m(-2) (for reported winter conditions) to similar to30 W m(-2) for inter-monsoon and to similar to15 W m(-2) for summer monsoon seasons. These will have implications on regional climate forcing.