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We analyzed impacts of the 2014–2015 Pacific Warm Anomaly and 2015–2016 El Niño on physical and biogeochemical variables at two southern California Current System moorings (CCE2, nearshore upwelling off Point Conception; CCE1, offshore California Current). Nitrate and Chl‐afluorescence were <1 μM and <1 Standardized Fluorescence Unit, respectively, at CCE2 for the entire durations of the Warm Anomaly and El Niño, the two longest periods of such low values in our time series. Negative nitrate and Chl‐aanomalies at CCE2 were interrupted briefly by upwelling conditions in spring 2015. Near‐surface temperature anomalies appeared simultaneously at both moorings in spring 2014, indicating region‐wide onset of Warm Anomaly temperatures, although sustained negative nitrate and Chl‐aanomalies only occurred offshore at CCE1 during El Niño (summer 2015 to spring 2016). Warm Anomaly temperature changes were expressed more strongly in near‐surface (<40 m) than subsurface (75 m) waters at both moorings, while El Niño produced comparable temperature anomalies at near‐surface and subsurface depths. Nearshore Ωaragoniteat 76 m showed notably fewer undersaturation events during both warm periods, suggesting an environment more conducive to calcifying organisms. Planktonic calcifying molluscs (pteropods and heteropods) increased markedly in springs 2014 and 2016 and remained modestly elevated in spring 2015. Moorings provide high‐frequency measurements essential for resolving the onset timing of anomalous conditions and frequency and duration of short‐term (days‐to‐weeks) perturbations (reduced nitrate and aragonite undersaturation events) that can affect marine organisms. The 2014–2016 Pacific Warm Anomaly‐El Niño sequence significantly changed ocean conditions in the California Current System, but impacts of these anomalies on nutrients, chlorophyll‐a, and pH, and comparisons to past El Niño events, have not been well described. We examined 9 years (2010–2018) of data from two ocean moorings that provide hourly measurements at fixed locations in the southern California Current System, allowing us to determine both subseasonal and multiyear ecosystem changes. We found that nitrate (important for primary production) and chlorophyll‐awere anomalously low in nearshore waters throughout the Warm Anomaly and El Niño, suggesting nutrient delivery to the surface ocean was reduced. The Warm Anomaly and El Niño both produced anomalously warm shallow temperatures, but only El Niño produced significantly warmer waters below 50‐m depth. Aragonite, a carbonate mineral important for shell production in calcifying marine organisms, showed elevated saturation state during both the Warm Anomaly and El Niño, suggesting the two anomalous periods produced favorable calcification conditions. Planktonic shelled molluscs, a key component of the oceanic food web, increased during both the Warm Anomaly and El Niño. Our findings may help predict impacts of future anomalies on nutrient availability and biological responses in the California Current System. Nearshore nitrate and Chl‐afluorescence were near zero for most of the Warm Anomaly‐El Niño but increased briefly in spring 2015Temperature increases were surface‐intensified across the region during the Warm Anomaly, while El Niño also affected subsurface watersPlanktonic mollusc biomass was elevated in springs 2014 and 2016 in conjunction with Warm Anomaly and El Niño aragonite supersaturation

Variability of the flow across the Solomon Sea's southern entrance was examined using end point subsurface moorings and seafloor pressure sensors, reconstructed velocity profiles based on satellite‐derived surface velocity and bottom pressure‐derived subsurface velocity, and 1993–2017 proxy volume transport based on satellite altimetry. The reconstructed velocity correctly represents the fluctuating surface flow and subsurface core providing a high‐frequency continuous observing system for this sea. The mean equatorward volume transport over 0‐ to 500‐m depth layer is 15.2 Sv (1 Sv ≡ 106m3/s) during July 2012 to May 2017. The measurements resolve the full spectrum of the volume transport including energetic subseasonal variability that fluctuates by as much as 25 Sv over one week. At low‐frequency timescales, the study finds that linear Rossby waves forced by Ekman pumping in the interior of the Pacific influence not only seasonal fluctuations as found by previous studies but also interannual variability. As found previously, the El Niño–Southern Oscillation highly influences interannual volume transport. During the 2015/2016 El Niño, observations show the seasonal cycle to be suppressed from the second half of 2014, prior to the mature phase of the El Niño, to September 2016 along with an increase in across‐transect transport. At subseasonal timescales, local Ekman pumping and remote wind stress curl are responsible for a third of the subseasonal variance. The study highlights the importance of high‐frequency observations at the southern entrance of the Solomon Sea and the ability of a linear Rossby model to represent the low‐frequency variability of the transport. The Solomon Sea, located in the tropical southwest Pacific Ocean, is characterized by energetic currents that transport water from the subtropical South Pacific to the equatorial Pacific. In this study, we quantify the amount of water being transported through the Solomon Sea to understand how and why it changes over time. Over the observing period (July 2012 to May 2017), a mean water volume of 15.2 Sv (1 Sv ≡ 106m3/s) flows into the Solomon Sea at its southern entrance. The flow can change greatly over short time period (±25 Sv over 1 week) as being modified by winds over the Solomon Sea and further upstream over the Coral Sea. The observed inflow also has distinct interannual variability and a seasonal cycle with a minimum in March/April and a maximum in July/August. On these timescales, the flow fluctuates up to ±10 Sv as being influenced by the winds over the equatorial and tropical Pacific Ocean. During the 2015/2016 El Niño, our observations show that the equatorward flow via the Solomon Sea strengthens but the seasonal cycle is suppressed. We also showed that the flow can be efficiently monitored using only a pair bottom‐pressure sensors and satellite altimetry. The observations reveal energetic subseasonal flow (37% of total variance) into the Solomon Sea associated with local and remote windsRossby waves propagating from the central Pacific Ocean are well correlated with the inflow variability at seasonal and longer timescalesThe inflow strengthens and the seasonal cycle is suppressed during the 2015/2016 El Niño

Direct observations of the deep water circulation in the western Mediterranean Sea are presented, based on the analysis of autonomous profiling floats drifting at 1,200 and 1,900 m depth during the 1997–2002 period. The amount of water circulating in the basin is quantified, revealing several distinct gyres and boundary currents. It was also possible to follow the spreading of the newly formed Western Mediterranean Deep Water (nWMDW) and Tyrrhenian Deep Water (TDW), two main components of the deep water in the western Mediterranean, from their origin, based on their temperature and salinity signature. Both boundary currents and isolated eddies carrying the water into the interior are important for this. The deep circulation in the Mediterranean Sea is revealed by profiling floatsMultiannual average transports in the deep layers were estimatedThe spreading of the Western Mediterranean Deep Water and the Tyrrhenian Deep Water is characterized

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) O2content 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 O2uptake 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. Substantial uptake of oxygen is observed in the Labrador Sea during the 2014–2015 winterStronger oxygen sink compared to previous studies is linked to North Atlantic OscillationMany commonly used gas exchange parameterizations underestimate the observed flux dramatically

The Gravity Recovery and Climate Experiment (GRACE) satellite mission provides information on changes to the Earth's gravity field, including ocean mass. Long‐term trends in GRACE data are often considered unreliable due to uncertainties in the corrections made to calculate ocean mass from the raw measurements. Here, we use an independent estimate of ocean mass from satellite altimetry and in situ density data from five mooring sites and repeat hydrography to validate trends in GRACE over the North Atlantic, finding substantial agreement between the methods. The root‐mean‐square difference between ocean mass changes calculated with this method from the mooring data and those measured by GRACE is 3.5 mm per decade, much lower than the mean signal of 15.6 ± 1.8mm per decade for GRACE and 17.8 ± 5.2mm per decade for the altimetry‐mooring estimate. The GRACE ocean mass data are then used to study the change in the deep circulation of the North Atlantic between the 1 April 2002 to 31 March 2009 and 1 April 2010 to 31 March 2017 periods, revealing a large‐scale anticyclonic circulation anomaly off the North American coast. The change is associated with an increase of 13.9 ± 3.3Sv (1 Sv = 106m3s−1) of southward North Atlantic Deep Water flow in the interior between 30°N and 40°N, largely balanced by a northward anomaly of 10.7 ± 3.3Sv for the boundary circulation. This implies an increased importance of interior pathways compared to the Deep Western Boundary Current for the spreading of North Atlantic Deep Water, which constitutes the lower limb of the Atlantic Meridional Overturning Circulation. The Gravity Recovery and Climate Experiment (GRACE) satellites measure the Earth's gravity field, which can be used to study ocean currents. In this study, we validate long‐term trends in the data using independent ocean measurements to confirm that they reflect real changes in the ocean. In the Atlantic Ocean, North Atlantic Deep Water flows southward from its formation region near Greenland, spreading throughout the ocean basin. The flow of North Atlantic Deep Water is a crucial part of Earth's climate system, making it an important process to understand. Most of the water spreads southward in the so‐called Deep Western Boundary Current along the continental shelves of North America, but there is also a significant flow further offshore in the interior of the basin. We use the GRACE data to measure changes to these two pathways between the 2002–2009 and 2010–2017 periods. The results show that southward flow in the interior has strengthened during this time, with opposite changes near the continent. This marks a significant change to how this water spreads from the formation region. GRACE ocean mass trends are validated using mooring and altimetry dataChanges reveal decadal variability in the deep circulation of the North Atlantic oceanFlow of North Atlantic Deep Water in the interior strengthened compared to the boundary circulation

An international acoustic tomography experiment had been deployed in the western Mediterranean from January to October 1994. Seven transceivers spanned the region between France, Algeria, the Balearic Islands, and Sardinia/Corsica. The basin (maximum range 600 km) was ‘‘illuminated’’ by a single HLF‐5 source, the remaining sources had a shorter range but could communicate with their neighbors. Extensive hydrographic measurements and analysis of historical data accompanied the observations, including a large‐scale survey during deployment and recovery and a 2‐weekly XBT section along the main transmission path. Some paths went along/through complicated topography, and in addition a shipboard acoustic survey was carried out to study the propagation into shallow water. All instruments remained operational for the entire period, and 6 of the 7 had 100% return of received data. The receptions show a high S/N ratio with well‐resolved arrivals that agree well with acoustic propagation predictions. The seasonal variation of the travel times appears to be a good measure of the cycle of the large‐scale heat content. The 3‐D basin‐averaged temperature is estimated to have an accuracy of 3%–4% of the seasonal amplitude. A system like this, installed with shore‐cabled instruments, should be a valuable tool for monitoring interannual and climate‐scale water mass variability.

The Strait of Gibraltar Acoustic Monitoring Experiment was conducted during April–May 1996 to determine the feasibility of using acoustic methods to monitor the transport through the Strait of Gibraltar. Three different approaches to monitoring the flow were explored: (i) Traditional reciprocal ray differential travel times were obtained from three 2‐kHz transceivers. (ii) A horizontal array of two 2‐kHz receivers was installed on one of the acoustic paths across the Strait to test the feasibility of using horizontal arrival angles (phase differences) due to ray bending by the currents to measure the flow. (iii) A low‐frequency (250‐Hz) source transmitted to a 350‐m vertical receiving array on the opposite side of the Strait to begin to examine the feasibility of using modal analyses, matched‐field tomography, and full‐field inversion techniques to obtain data on the temperature and current fields. Our initial efforts are aimed at examining the stability of ray and mode propagation and quantifying the accuracy of existing acoustic propagation codes in the complex oceanographic environment that exists in the Strait. Extensive independent measurements of the temperature, salinity, and velocity fields along and perpendicular to the acoustic paths were obtained. [Work supported by ONR.]