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After a relaxation of the regional southward, upwelling‐favorable winds along the central California coast, warm water from the Santa Barbara Channel propagates northward as a buoyant plume. As the plume transits up the coast, it causes abrupt temperature changes and modifies shelf stratification. We use temperature and velocity data from 35 moorings north of Pt. Arguello to track the evolution of a buoyant plume after a wind relaxation event in October 2017. The moorings were deployed September–October 2017 and span a ∼30 km stretch of coastline, including nine cross‐shelf transects that range from 17 to 100 m water depth. The high spatial resolution of the data set enables us to track the spatiotemporal evolution of the plume, including across‐front temperature difference, cross‐shore structure, and propagation velocity. We observe an alongshore current velocity signal that takes ∼10 hr to propagate ∼25 km alongshore (∼0.7 m/s) and a temperature signal that takes ∼34 hr to propagate the same distance (∼0.2 m/s). The plume cools as it transits northward, leading to a decrease in the cross‐front temperature difference and the reduced gravity (g'). The plume's propagation velocity is nonuniform in space and time, with accelerations and decelerations unexplained by the alongshore reduction in g' or advection by tidal currents. As the plume reaches the northernmost part of the mooring array, its temperature variability is obscured by internal waves, a prominent feature in the region. We focus on one relaxation event but observe five other similar events over the 2 months record. Plain Language Summary: Coastal ocean conditions along the US west coast are affected by strong, regional‐scale winds that predominantly blow southward along California. Under "normal" conditions, these winds and other ocean processes cause a large difference between water temperature in the Santa Barbara Channel (warm) and outside the channel to the northwest (cold). When the regional winds weaken, warm water exits the channel as a buoyant plume and moves northward up the coast. Similar plumes occur elsewhere around the world, and these plumes have important ecological impacts because they transport larvae of coastal marine species. Using instruments in the water at 35 sites north of Pt. Arguello, we study how warm plumes travel along a ∼30 km stretch of coastline. Six of these northward‐propagating warm plumes were observed September–October 2017, and we primarily describe one event in detail. We study the speed the warm plume travels, how that speed changes in space and time, and why the speed is not constant. We observe that the plume water cools as it moves northward, resulting in increased difficulty identifying the plume in the northern sites. We also find that the plume's warm signature can be obscured by similar warm signals caused by the tides. Key Points: After a wind relaxation, there are two northward propagating signals: an alongshore velocity signal (∼0.7 m/s) and a warm signal (∼0.2 m/s)The warm buoyant plume becomes cooler and thinner as it propagates alongshore, resulting in a weakening of the cross‐front temperature differenceThe nonuniform propagation velocity of the warm plume is not explained by tidal advection or plume cooling [ABSTRACT FROM AUTHOR]

Ocean monitoring is an expensive and time consuming endeavor, but it can be made more efficient through the use of teams of autonomous robots. In this paper, we present a system for the autonomous identification and tracking of ocean fronts by coordinating the sampling efforts of a heterogeneous team of autonomous surface vehicles (ASVs) and autonomous underwater vehicles (AUVs). The primary contributions of this study are (1) our algorithm for performing autonomous coordination using general autonomy principles: Sequential Allocation Monte Carlo Tree Search (SA‐MCTS) which incorporates domain knowledge into the environmental estimation through both augmenting a standard Gaussian process with a nearest neighbors prior and planning in a drifting reference frame, (2) our decision support user interface to help human operators oversee the autonomous system, and (3) the demonstration of the system's operation in a 2‐week long deployment in the Gulf of Mexico using a heterogeneous team of four Slocum gliders and two robotic ocean surface samplers. With these contributions, we aim to bridge the gap between state of the art autonomy algorithms and marine vehicle planning methods that have been tested in large‐scale field trials. This paper presents the first deployment of a general, heuristic‐based, multi‐robot coordination algorithm for an extended sampling mission. [ABSTRACT FROM AUTHOR]

Observations have suggested a trend of decreasing dissolved oxygen (DO) and increasing spiciness in summertime middepth slope waters and bottom shelf waters along the United States west coast over the past 50 years, but they have also demonstrated a large amount of interannual and decadal variability. Shelf bottom water and slope water properties can be influenced by both local and remote effects, including changes in circulation or changes in the characteristics of the source waters supplying the region. A regional-scale, coupled physical biogeochemical model has been developed to simulate seasonal-to-decadal scale variability along the US west coast to discern the physical dynamics behind these spatial and temporal patterns. A simulation run from 1981 to 2006 with forcing that incorporates the larger scale interannual trends reproduces the development of low DO late in the upwelling season, the considerable interannual variability and the reported tendency toward a shoaling, more spicy, and oxygen-depleted, northern California Undercurrent (CU). Whereas the trend in spiciness in the model results from increased influence of equatorial relative to subarctic source waters, the decreases in DO are found to additionally be a consequence of local biogeochemical processes. In order to better understand the interannual variability, years of the simulation were classified into four groups based on intensity of upwelling forcing and undercurrent strength. Slope water characteristics, shelf-slope exchange, and slope-basin exchange were compared across the four cases. Years with both strong upwelling and a strong undercurrent generated the most negative anomalies in slope-water DO late in the upwelling season. [ABSTRACT FROM AUTHOR]

Various ocean-climate models driven by increased greenhouse gases and higher temperatures predict a decline in oceanic dissolved oxygen ( DO) as a result of greater stratification, reduced ventilation below the thermocline, and decreased solubility at higher temperatures. Since spreading of low oxygen waters is underway and predicted to increase, understanding impacts on higher trophic levels is essential. Within the California Current System, shoaling of the oxygen minimum zone ( OMZ) is expected to produce complex changes. Onshore movement of the OMZ could lead to habitat compression for species with higher oxygen requirements while allowing expansion of species tolerant of low bottom DO. As part of annual groundfish surveys, we sampled catch across a range of conditions from the upper to the lower limit of the OMZ and shoreward across the continental shelf of the US west coast. DO ranged from 0.02 to 4.25 mL L−1 with 642 stations (of 1020 sampled) experiencing hypoxic conditions in 2008-2010. Catch and species richness exhibited significant and positive relationships with near-bottom oxygen concentration. The probability of occurrence was estimated for four species (spotted ratfish, petrale sole, greenstriped rockfish and Dover sole) using a binomial Generalized Additive Model. The models for each species included terms for position, day of the year, salinity, near-bottom temperature and the interaction term between depth and near-bottom DO. Spotted ratfish and petrale sole were sensitive to changes in near-bottom oxygen, while greenstriped rockfish and Dover sole show no changes in probability of occurrence in relation to changes in oxygen concentration. [ABSTRACT FROM AUTHOR]

In August 2007, as part of the NOAA National Marine Fisheries Service (NMFS) West Coast Groundfish Bottom Trawl Survey, we examined the biomass of demersal organisms in a known hypoxic area off the Oregon coast. Although observed each summer, the intensity of hypoxia has varied annually (2002–2007) with the greatest temporal and spatial extent noted in 2006. In 2007 we identified the geographic extent of the hypoxic zone and sampled 17 stations along two depth contours (50 and 70 m) within the area. A Sea-Bird SBE 19 plus equipped with a dissolved oxygen (DO) sensor was attached to the bottom trawl to monitor oxygen concentration during each tow. Bottom DO concentrations at all stations were hypoxic with means along the tow tracts ranging from 0.43 to 1.27 mL L−1. Total catch per unit effort (ln CPUE, kg hectare−1) and species diversity (number of species, N) were significantly and positively related to oxygen concentration along the hypoxic gradient. In addition, CPUE (natural log-transformed) for eight fish species and five benthic invertebrate species were significantly and positively related to bottom oxygen concentration within the hypoxic region. Condition factors for five fish species, as well as Dungeness crab ( Cancer magister) increased with increased bottom oxygen levels along the hypoxic gradient. Historical catch (2003–2006) within the hypoxic zone indicates that biomass was significantly lower in 2006, the year with the lowest bottom DO levels, relative to other years. [ABSTRACT FROM AUTHOR]

A long-standing issue in marine biology is identifying spatial scales at which populations of sessile adults are connected by planktonic offspring. We examined the genetic continuity of the acorn barnacle Balanus glandula, an abundant member of rocky intertidal communities of the northeastern Pacific Ocean, and compared these genetic patterns to the nearshore oceanography described by trajectories of surface drifters. Consistent with its broad dispersal potential, barnacle populations are genetically similar at both mitochondrial (cytochrome oxidase I) and nuclear (elongation factor 1-alpha) loci across broad swaths of the species’ range. In central California, however, there is a striking genetic cline across 475 km of coastline between northern and southern populations. These patterns indicate that gene flow within central California is far more restricted spatially than among other populations. Possible reasons for the steep cline include the slow secondary introgression of historically separated populations, a balance between diversifying selection and dispersal, or some mix of both. Geographic trajectories of oceanic drifters closely parallel geographical patterns of gene flow. Drifters placed to the north (Oregon; ∼44°N) and south (Santa Barbara, California; ∼34° N) of the cline disperse hundreds of kilometres within 40 days, yet over the long-term their trajectories never overlapped. The lack of communication between waters originating in Oregon and southern California probably helps to maintain strong genetic differentiation between these regions. More broadly, the geographical variation in gene flow implies that focusing on species-level averages of gene flow can mask biologically important variance within species which reflects local environmental conditions and historical events. [ABSTRACT FROM AUTHOR]