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Superimposed on long-term ocean acidification are ocean acidity extremes (OAXs), i.e., periods of unusual acidity in the marine environment. Such extremes form through the interplay of the various spatio-temporal scales of variability associated with the ocean’s carbonate system, ranging from multi-decadal trends to subseasonal dynamics. Using a high-resolution regional ocean model coupled to a biogeochemical-ecosystem model (ROMS-BEC) we assess the role of five mechanisms associated with different scales of variability – namely atmospheric CO2 rise, the decadal North Pacific Gyre Oscillation (NPGO), the interannual El-Niño-Southern Oscillation (ENSO), seasonal upwelling, and mesoscale eddies – in the occurrence of OAXs in a 300 km nearshore band along the U.S. West Coast and the Alaskan coast over the period 1984 to 2019. We find that the annual fraction of the upper 250 m depth that is hit by OAXs increases at a rate of 0.16 % units.μatm-1 driven by the increase in atmospheric CO2 concentration. In addition, our analysis reveals that Pacific climate variability substantially modulates OAXs occurrence on interannual timescales. The fraction of the upper 250 m depth that is hit by OAXs increases by 0.53 % units per unit decrease in the ENSO index, and 0.39 % units per unit increase in the NPGO index. Last but not least, we find that seasonal upwelling and mesoscale cyclonic eddies are key regional drivers of OAXs along the U.S. West Coast. Our results show that coastal upwelling forms intense and shallow OAXs near the coast, while mesoscale cyclonic eddies drive large and long-lasting OAXs that propagate over hundreds of kilometers from the coast to the offshore. Altogether, our results quantify the respective imprint of five mechanisms associated with different scales of variability on the occurrence of OAXs in coastal regions. This knowledge opens new perspectives for improving the predictability of OAXs in the highly productive coastal regions of the northeast Pacific.

In recent decades, the Eastern Pacific has been subject to many pronounced marine heatwaves (MHWs), with far-reaching consequences for marine ecosystems. As MHWs are commonly detected at the sea surface, little is known about their vertical structure, let alone the temporal variability of this structure. To fill this gap, we detect and characterise vertically extended MHWs within a high-resolution model hindcast simulation (1979-2019) of the Eastern Pacific. Considering the vertical dimension in the MHW detection furthermore enables the tracking of vertical MHW propagation. We find that 71% of MHWs are on average confined to the mixed layer, while 29% reach at least 10m below. By clustering the MHWs, we identify four main vertical propagation patterns. While the majority of MHWs remains at the surface throughout their lifetime, 18% (13%) of MHWs subduct beneath (shoal towards) the surface, while 12% rather sit beneath the surface and exhibit multi-surfacing behaviour. As a consequence of the vertical propagation, MHWs affect upper ocean ecosystems substantially longer than diagnosed from the sea surface (40 vs. 30 days on average).In the mid-latitude Northeast Pacific, we find a seasonal cycle in the vertical MHW propagation clusters. We find that wintertime MHWs can detrain from the mixed layer, persist in the seasonal thermocline and re-entrain into the ML at a later stage. This finding agrees well with previous work on the role of the re-emergence phenomenon of sea surface temperature anomalies in the North Pacific and suggests potential sources of predictability for MHWs at the sea surface. At lower latitudes, we find that interannual variability associated with the El Niño-Southern Oscillation strongly dominates any seasonality in the occurrence of the different MHW clusters. Lastly, we find that accounting for the vertical MHW propagation almost doubles the average Eastern Pacific area affected by MHWs, compared to the surface only perspective. These new insights regarding MHW depth structures and their temporal variability mark an important step towards a better understanding of MHW drivers and the consequences of MHWs for marine ecosystems.

Since it was recognised that the Southern Ocean plays a crucial role in global climate, the region has generally been understood in a zonally symmetric framework. While this simplification has provided valuable insight, recent work suggests that significant zonal asymmetries exist in several key parameters such as SST, mixed layer depth and air-sea CO2 flux. This is true both for the mean state and for changes at multiple time scales. Of particular interest here are changes in ocean heat content (ΔOHC) over the past three decades. Using an eddy-permitting ocean model forced by ERA5 reanalysis, we find significant asymmetries in ΔOHC both within and north of the ACC, which is robustly reflected in a suite of hindcast and reanalysis models, as well as observation based temperature reconstructions. In our model, asymmetry stems largely from a southward displacement of ΔOHC in the Indian basin, where warming occurs primarily within ACC, as opposed to north of it in the Atlantic and Pacific. However, significant asymmetries are also found within the sea ice zone south of 60o S, where the Ross Sea warms to a much greater degree than other basins. In order to better understand the sources of this asymmetric warming, we run several model experiments which decompose the total OHC into components originating from wind, heat and freshwater flux changes. We find roughly equal contributions from wind and surface heat flux north of the ACC, with asymmetric changes in the westerlies driving anomalous convergence of heat. Within and south of the ACC all three forcings play an important role, although this depends strongly on the basin. Overall, we conclude that much of the asymmetries in ΔOHC originate from asymmetries in the surface flux changes, with an important secondary role played by variability in the mean state. These findings have two important implications. First, studies which only consider zonally averaged quantities will likely mask significant variability, and therefore miss important regional and local processes. Second, the impact of multi-decadal climate variability on the Southern Ocean is not manifested in a zonally symmetric fashion, which may have important implications for future changes.

Marine extreme events can be detrimental to organisms and ecosystems across the global ocean. Marine heatwaves (MHW), ocean acidity extremes (OAX) and low oxygen extremes (LOX) occur everywhere, superimposed on the already changing trends of temperature, pH, and oxygen. When such extremes concurrently occur in the vertical column, the habitable space for marine organisms can be severely reduced. We use daily output from a hindcast simulation with the Community Earth System Model coupled with Biological Elemental Cycling (CESM-BEC) for the period 1961-2020 to characterise such compound extremes. Extreme conditions are identified on a moving baseline with the 95th or 5th percentile, and an additional absolute threshold of 150 μM for low oxygen conditions. To investigate compound events in the vertical dimension, at least 50 m out of the top 300 m is required to be extreme with respect to each stressor. Such an event is termed a column-compound extreme event (CCX). On average, 1% of the global ocean volume is occupied by CCXs and up to 5% at maximum. On a fixed baseline these values increase to 8% and 27% respectively. CCXs decrease habitable space by up to 75% and have high intensity index of more than 2 in many regions around the globe. El Niño-Southern Oscillation events are found to be strongly associated with CCXs in the tropical and subtropical Pacific, but also other ocean basins through teleconnections. The global volume of CCXs is expected in increase in the future, exacerbating impacts and reducing habitable space of marine organisms.

The acidification of the ocean (OA) increases the frequency and intensity of ocean acidity extreme events (OAXs), but this increase is not occurring homogeneously in time and space. Here we use daily output from a hindcast simulation with a high-resolution regional ocean model coupled to a biogeochemical-ecosystem model (ROMS-BEC) to investigate this heterogeneity in the progression of OAX in the upper 250 m of the Northeast Pacific from 1984 to 2019. We focus on the temporal and spatial changes in OAX using a relative threshold approach and using a fixed baseline reflecting the initial conditions. Concretely, conditions are considered extreme when the local hydrogen ion concentration ([H+]) exceeds the 99th percentile of the [H+] distribution of the baseline simulation where atmospheric CO2 was held at its 1979 level. Within the 36 years of our hindcast simulation, the increase in atmospheric CO2 causes a strong increase in OAX throughout the upper 250 m, but most accentuated near the surface. On average across the entire Northeast Pacific, for every additional 10 μatm of CO2 in the atmosphere, OAXs occupy an additional 6.3 % of the upper 250 m depth, last 7.6 days longer, and are 0.18 nmol L−1 (~ −0.006 pH units) more intense. This causes the OAXs to occupy at the end of the simulation a more than 10-times larger volume. The more than 11-fold increase in length, and the strong increase in the number of extreme days per year causes 88 % of the surface area in 2019 to experience near permanent extreme conditions. Finally, the model simulates a more than 6-fold intensification of the OAXs, causing also the intensity of the events with return periods of 10 years or more to increase by more than 80 %. Superimposed on these overall trends are very substantial spatial and temporal differences in these changes. The fraction of the volume identified as extreme across the top 250 m increases in the Central Northeast Pacific up to 160-times, while the deeper layers of the nearshore regions experience "only" a 4-fold increase. Throughout the upper 50 m of the Northeast Pacific, OAXs increase relatively linearly with time, but sudden rapid increases in yearly extreme days and OAX duration are simulated to occur in the thermocline of the Central Northeast Pacific. These differences largely emerge from the large spatial differences in the magnitude and nature of variability in [H+], with the transition between the rather variable thermocline waters of the Offshore Northeast Pacific and the very stable waters of the Central Northeast Pacific causing a very sharp transition in the occurrence of OAX. This transition is caused by the limited offshore reach of offshore propagating eddies that are the dominant driver of OAX in the Northeast Pacific. As the OAXs become more extreme, more of them also become undersaturated with respect to aragonite (ΩA < 1), i.e., become corrosive. In the final year of our hindcast, we find that below 100 m OAXs are characterized by corrosive conditions across a wide stretch of the region offshore of the U.S. and Canadian Coasts. The spatially and temporal heterogeneous increases in OAX, including the abrupt appearance of extremes, likely have negative effects on the ability of marine organisms to adapt to the progression of OA and its associated extremes.

The Southern Ocean is well recognised as globally the most important region for the uptake and storage of excess heat (Q`) and carbon (C`) resulting from anthropogenic CO2 emissions. Although the processes governing the transport and storage of Q` and C` are tightly connected, the near surface boundary conditions of the two perturbation tracers are very different. That is, the spatial distribution of C` in the atmosphere is rather homogenous, while the uptake of Q` is characterised by strong horizontal gradients and temporal variability ranging from seasonal to interannual and decadal. The effect this difference has on the uptake and storage patterns of Q` and C` has received relatively little attention, especially when compared to the role of ocean circulation changes. In order to address this, we utilise a regional ocean biogeochemical model (ROMS-BEC) forced with an atmospheric reanalysis (ERA5) and perform a suite of model experiments. A first set of experiments quantifies changes in C` and Q` over the period 1979 -2019, comparing the model results with observation-based estimates. Here we find that the model is able to reproduce the main features of the observed Q` and C` storage patters: a region of enhanced heat storage at ~40oS and down to 1200m, with carbon storage peaking in the surface layer (~200m) north of 40oS and decreasing poleward and with depth. A second set of experiments aims to isolate the role of spatial and temporal variability of net surface heat flux (SHF) in driving changes in Q`, with the resulting storage patterns then compared to those derived for C`. We find that for C` the storage pattern is driven largely by the uptake of anthropogenic CO2 , with a small contribution from circulation changes. In contrast, the storage pattern of Q` appears not to be strongly related to trends in SHF, suggesting that the mean SHF spatial distribution, as well as circulation changes may play a more prominent role. The SHF trends themselves are highly spatially heterogenous, and act to reduce the magnitude of the zonally integrated heat storage over the simulated period. However, we find that there are significant regional differences, with a modest increase in storage in the Pacific and Atlantic sectors being offset by a much stronger reduction in the Indian sector. Overall, we develop a conceptual framework for understanding the potential (de)coupling between oceanic uptake and storage of heat and carbon within the unique context of the Southern Ocean.

The Canary upwelling system (CanUS) is a productive coastal region characterized by strong seasonality and an intense offshore transport of organic carbon (Corg) to the adjacent oligotrophic offshore waters. There, the respiration of this Corg substantially modifies net community production (NCP). While this transport and the resulting coupling of the biogeochemistry between the coastal and open ocean has been well studied in the annual mean, the temporal variability, and especially its seasonality, has not yet been investigated. Here, we determine the seasonal variability of the offshore transport of Corg, its mesoscale component, latitudinal differences, and the underlying physical and biological drivers. To this end, we employ the Regional Ocean Modeling System (ROMS) coupled to a nutrient–phytoplankton–zooplankton–detritus (NPZD) ecosystem model. Our results reveal the importance of the mesoscale fluxes and of the upwelling processes (coastal upwelling and Ekman pumping) in modulating the seasonal variation of the offshore Corg transport. We find that the region surrounding Cape Blanc (21∘ N) hosts the most intense Corg offshore flux in every season, linked to the persistent, and far reaching Cape Blanc filament and its interaction with the Cape Verde Front. Coastal upwelling filaments dominate the seasonality of the total offshore flux up to 100 km from the coast, contributing in every season at least 80 % to the total flux. The seasonality of the upwelling modulates the offshore Corg seasonality hundreds of kilometers from the CanUS coast via lateral redistribution of nearshore production. North of 24.5∘ N, the sharp summer–fall peak of coastal upwelling results in an export of more than 30 % of the coastal Corg at 100 km offshore due to a combination of intensified nearshore production and offshore fluxes. To the south, the less pronounced upwelling seasonality regulates an overall larger but farther-reaching and less seasonally varying lateral flux, which exports between 60 % and 90 % of the coastal production more than 100 km offshore. Overall, we show that the temporal variability of nearshore processes modulates the variability of Corg and NCP hundreds of kilometers offshore from the CanUS coast via the offshore transport of the nearshore production., Biogeosciences, 18 (8), ISSN:1726-4170

The drop of ruminal pH and heat are common physicochemical stressors challenging ruminal microbiota, nutrient digestion and cattle performance. We characterized the ruminal microbiota and digestive activity in response to different pH (6.0 and 6.6) and temperature (39.5 and 42 °C), as well as established the effective dose of alkaloid supplementation (0, 0.088 and 0.175% of feedstock DM) to modulate ruminal fermentation under these conditions. The acidotic condition decreased microbial diversity and abundances of minor bacterial families whereas most of the highly abundant families like Lactobacillaceae, Prevotellaceae, and Bifidobacteriaceae thrived under the stress. Abundances of all three methanogenic archaea taxa detected increased with heat, as did methane production. However, while Methanomassiliicoccaceae benefited from the low pH, Methanomicrobiaceae diminished and methane production decreased. The low dose of alkaloid addition shifted the fermentation to more propionate and less acetate and the high dose decreased methane and ammonia concentration under the low pH. In conclusion, physicochemical stressors shape the microbial community and function. Mixed alkaloid supplementation facilitates the activity of rumen microbial community under acidotic stress.

Much of the Southern Ocean surface south of 55° S cooled and freshened between at least the early 1980s and the early 2010s. Many processes have been proposed to explain the unexpected cooling, including increased winds or increased surface freshwater fluxes from either the atmosphere or glacial meltwater. However, these mechanisms so far failed to fully explain the surface trends and the concurrently observed warming of the subsurface (100 to 500 m). Here, we argue that these trends are predominantly caused by an increased wind-driven northward transport of sea ice, enhancing the extraction of freshwater near Antarctica and releasing it in the open ocean. This conclusion is based on factorial experiments with a regional ocean model. In all experiments with an enhanced northward transport of sea ice, the open-ocean surface between the Subantarctic Front and the sea-ice edge is cooled by strengthening the salinity dominated oceanic stratification. The strengthened stratification reduces the downward mixing of cold surface water and the upward heat loss of the warmer waters below, thus warming the subsurface. This sea-ice induced subsurface warming mostly occurs around West Antarctica, where it likely enhances ice-shelf melting. Moreover, it could account for about 8±2% of the global ocean heat content increase between 1982 and 2011. Antarctic sea-ice changes thereby may have contributed to the slowdown of global surface warming over this period. The important role of sea-ice in driving changes in the high-latitude Southern Ocean are robust across all considered sensitivity cases, although their magnitude is sensitive to the forcing and the role of salinity in controlling the vertical stratification in the mean state. It remains yet unclear whether these sea-ice induced changes are associated with natural variability or a response to anthropogenic forcing.

Molassed sugar beet pulp (Bp) is a human inedible by-product of the sugar industry being a suitable dietary energy alternative to grains particularly in terms of increasing the net food production efficiency of high-producing dairy cattle. However, there are concerns that feeding large amounts of Bp can limit cow’s feed intake, jeopardizing both the production performance and metabolic health especially of high-producing dairy cows that have high energy needs. In the present study dietary inclusion of Bp as a substitute for maize grain was tested in a longitudinal block-randomized experimental design in early lactation high-yielding Simmental cows. The Bp inclusion rates were 0 g/kg (i.e., no Bp inclusion as control), 120 g/kg (12Bp), or 240 g/kg (24Bp) on a dry matter basis. The replacement of maize grain with Bp reduced the human edible input from 135.4 MJ GE/d in the control diet to 50.7 MJ GE/d in the 24Bp diet (P 0.05), whereas dietary fibre digestibility was linearly improved (P = 0.038) with Bp feeding, indicating enhanced rumen health and functioning with Bp feeding. In conclusion, feeding molassed sugar beet pulp as partial substitution of maize until 240 g/kg is a viable alternative that can improve net food production without impairing the cows’ production performance and the metabolic health status of cows while improving the digestibility of fibre.

Background: Molassed sugar beet pulp (Bp) is a viable alternative to grains in cattle nutrition for reducing human edible energy input. Yet little is known about the effects of high inclusion rates of Bp on rumen microbiota. This study used an in vitro approach and the quantitative polymerase chain reaction technique to establish the effects of a graded replacement of maize grain (MG) by Bp on the ruminal microbial community, fermentation profile and nutrient degradation.; Results: Six different amounts of Bp (0-400 g kg-1 ), which replaced MG in the diet, were tested using the in vitro semi-continuous rumen simulation technique. The increased inclusion of Bp resulted in greater dietary content and degradation of neutral detergent fibre (P < 0.01). Further, Bp feeding enhanced (P < 0.01) the abundance of genus Prevotella and shifted (P < 0.01) the short-chain fatty acid patterns in favour of acetate and propionate and at the expense of butyrate. A total replacement of MG with Bp resulted in an increased daily methane production (P < 0.01).; Conclusion: Results suggest positive effects of the replacement of MG by Bp especially in terms of stimulating ruminal acetate and propionate fermentation. However, high replacement rates of Bp resulted in lowered utilization of ammonia and higher ruminal methane production. © 2017 Society of Chemical Industry.; © 2017 Society of Chemical Industry.

Feeding of industrial by-products such as sugar beet pulp (Bp) is an economically viable option in dairy production, but high inclusion rates might impair feed intake and performance of the cows. The present meta-analysis was performed to evaluate inclusion of Bp in dairy cow diets taking into account inclusion rate of Bp, feed intake and production levels of the cows, concentrate level in the diet and replacement aim of Bp (i.e., grain type and forage replaced). Effects on dry matter intake (DMI), ruminal fermentation, and milk production variables as well as on net food production, as a measure of sustainability, were determined using meta-analysis and meta-regression approaches. Data were extracted from 34 different studies published from 1990 to 2016, comprising a total of 103 dietary treatments. The effect of Bp on DMI depended largely ( P = 0.016) on the feed intake level of cows. DMI decreased with increasing Bp inclusion level in cows with a high feed intake level (>3.5% of BW), but not in cows with a low intake level (≤3.5% of BW), noted by an interaction between Bp level and feed intake level ( P = 0.015). Bp inclusion had no effect on milk yield ( P = 0.514) but increased milk fat yield ( P = 0.004) and fat-corrected milk yield ( P = 0.002). Effects of Bp on milk production variables were independent of the dietary concentrate level as well as the replacement aim. Ruminal pH increased ( P = 0.046) but only when Bp was fed at a level of >200 g/kg of diet DM. There were interactions between the Bp inclusion and the dietary concentrate level for molar percentages of propionate ( P = 0.008) and butyrate ( P = 0.021) and, to a lesser extent, for acetate ( P = 0.057), with acetate and propionate being altered by Bp only in high concentrate diets. All variables related to net food production including kg milk/MJ human edible energy input ( P = 0.002) or g milk protein/g human edible protein input ( P = 0.027) were strongly improved by feeding of Bp. In conclusion, the effect of Bp as a feedstuff for dairy cows depends on the cow’s feed intake and production level, whereby high inclusion rates of Bp seem to be particularly beneficial in cows in which the feed intake level does not exceed 3.5% of BW.

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.

High starch lactation diets not only enhance the risk of subacute ruminal acidosis but also of hindgut acidosis, which increases the risk of dysbiosis and the depression of fiber degradation. We recently showed that replacing corn with molassed sugar beet pulp (Bp) improved fiber degradation in high-producing dairy cattle, possibly because of an improvement of rumen and hindgut conditions for microbes by Bp feeding. However, little is known about the effects of high inclusion rates of Bp on hindgut microbes and fermentation. Thus fecal grab samples were taken from 18 high-yielding Simmental cows after 28 d of feeding 3 different levels of Bp (n = 6) for bacterial 16S rRNA amplicon sequencing. In addition, the reticular pH was continuously monitored with indwelling sensors and eating and ruminating behavior was evaluated with noseband sensors. The Bp inclusion rates were 0 g/kg (i.e., no Bp inclusion as control, CON), 120 g/kg (12Bp), or 240 g/kg (24Bp) replacing corn grain and limestone on a dry matter basis. The amount of time spent eating and ruminating was unaffected by Bp level, and the daily fluctuation in the reticular pH was reduced by 25% with Bp inclusion from 0.8 in the CON diet to 0.6 in 24Bp fed animals. Also, the fecal pH tended to increase with dietary Bp inclusion. Fecal acetate production showed a quadratic tendency with the lowest concentration (58.9%) of the total short-chain fatty acid in the 12Bp treatment. Inclusion of Bp up to 24% of the diet decreased the fecal butyrate proportion by 27%. The Shannon diversity index was increased from 5.50 to 8.09 with dietary Bp inclusion indicating increased species diversity. Of the 200 most abundant operational taxonomic units, 25 were increased by dietary Bp inclusion, whereas 15 were decreased and 7 were quadratically affected. The second most abundant group was proposed taxon "CF231" of the family Paraprevotellaceae. Although it accounted for only 2.52% of the operational taxonomic units in the CON diet, it was increased by 64% with dietary Bp inclusion. The largest relative change in the abundance was found for the genus Fibrobacter that increased more than 14-fold from 0.04% (CON) to 0.66% (24Bp). In conclusion, feeding molassed sugar beet pulp as partial substitution of corn up to 240 g/kg is a viable alternative that promotes ruminal and hindgut fermentation by supporting physiological pH and bacterial diversity.

Although mesoscale ocean eddies are ubiquitous in the Southern Ocean, their spatial and seasonal association with phytoplankton has to date not been quantified in detail. To this end, we identify over 100,000 eddies in the Southern Ocean and determine the associated phytoplankton biomass anomalies using satellite-based chlorophyll-a (Chl) as a proxy. The mean eddy associated Chl anomalies (𝛿Chl) exceed &pm;10 % over wide regions. The structure of these anomalies is largely zonal, with cyclonic, thermocline lifting, eddies having positive anomalies in the subtropical waters north of the Antarctic Circumpolar Current (ACC) and negative anomalies along the ACC. The pattern is similar, but reversed for anticyclonic, thermocline deepening eddies. The seasonality of 𝛿Chl is weak in subtropical waters, but pronounced along the ACC, featuring a seasonal sign switch. The spatial structure and seasonality of 𝛿Chl can be explained largely by lateral advection, especially eddy-stirring. A prominent exception is the ACC region in winter, where 𝛿Chl is consistent with a modulation of phytoplankton light exposure caused by an eddy-induced modification of the mixed layer depth. The clear impact of eddies on phytoplankton may implicate a downstream effect on Southern Ocean biogeochemical properties, such as mode water nutrient contents.

Many aspects of the coupling between the ocean and atmosphere at the mesoscale (on the order of 20–100 km) remain unknown. While recent observations from the Southern Ocean revealed that circular fronts associated with oceanic mesoscale eddies leave a distinct imprint on the overlying wind, cloud coverage, and rain, the mechanisms responsible for explaining these atmospheric changes are not well established. Here the atmospheric response above mesoscale ocean eddies is investigated utilizing a newly developed coupled atmosphere–ocean regional model [Consortium for Small-Scale Modeling–Regional Ocean Modelling System (COSMO-ROMS)] configured at a horizontal resolution of ~10 km for the South Atlantic and run for a 3-month period during austral winter of 2004. The model-simulated changes in surface wind, cloud fraction, and rain above the oceanic eddies are very consistent with the relationships inferred from satellite observations for the same region and time. From diagnosing the model’s momentum balance, it is shown that the atmospheric imprint of the oceanic eddies are driven by the modification of vertical mixing in the atmospheric boundary layer, rather than secondary flows driven by horizontal pressure gradients. This is largely due to the very limited ability of the atmosphere to adjust its temperature over the time scale it takes for an air parcel to pass over these mesoscale oceanic features. This results in locally enhanced vertical gradients between the ocean surface and the overlying air and thus a rapid change in turbulent mixing in the atmospheric boundary layer and an associated change in the vertical momentum flux.

Much of the observed interannual variability in the physical and biogeochemical state of the California Current System (CalCS) is associated with El Nino Southern Oscillation. Yet it is unclear whether this is primarily a result of atmospheric teleconnections forcing the ocean locally through changes in wind and fluxes of heat and freshwater, or whether this is a consequence of oceanic interior processes that transport tropical variability through, e.g., coastally trapped waves to the region. Here we investigate the relative contribution of these two mechanisms in the CalCS using a novel setup of the Regional Oceanic Modeling System coupled to a biogeochemical/ecological model. We conducted a hindcast simulation over the period 1979–2013 and contrast the results with those from sensitivity simulations with climatological atmospheric boundary conditions either for the U.S. West Coast or the rest of the Pacific. We find that remote forcing dominates the variability of the physical state in the nearshore region of the CalCS, explaining up to 80% of monthly mean sea-surface height and temperature variability. In contrast, local processes tend to drive variations in the biogeochemical/ecological state, particularly along central and northern California, explaining up to 50% of the observed surface variability. Most of the remote forcing is a consequence of coastally trapped waves that travel northward at speeds of approximately 230 km d−1, and thereby alter sea-level height, thermocline structure, and upwelling along California. Biogeochemically active tracers respond to this remote forcing as well, especially at depth, but are more strongly modulated by local atmospheric forcing, especially variations in upwelling-favorable winds.

Molassed sugar beet pulp (Bp) is a viable alternative to grains in cattle nutrition for reducing human edible energy input. Yet little is known about the effects of high inclusion rates of Bp on rumen microbiota. This study used an in vitro approach and the quantitative polymerase chain reaction technique to establish the effects of a graded replacement of maize grain (MG) by Bp on the ruminal microbial community, fermentation profile and nutrient degradation.Six different amounts of Bp (0-400 g kgResults suggest positive effects of the replacement of MG by Bp especially in terms of stimulating ruminal acetate and propionate fermentation. However, high replacement rates of Bp resulted in lowered utilization of ammonia and higher ruminal methane production. © 2017 Society of Chemical Industry.

Owing to the turbulent nature of the ocean, mesoscale eddies are omnipresent. The impact of these transitory and approximately circular sea surface temperature fronts on the overlying atmosphere is not well known. Stationary fronts such as the Gulf Stream have been reported to lead to pronounced atmospheric changes1, 2. However, the impact of transient ocean eddies on the atmosphere has not been determined systematically, except on winds and to some extent clouds3, 4, 5, 6. Here, we examine the atmospheric conditions associated with over 600,000 individual eddies in the Southern Ocean, using satellite data. We show that ocean eddies locally affect near-surface wind, cloud properties and rainfall. The observed pattern of atmospheric change is consistent with a mechanism in which sea surface temperature anomalies associated with the oceanic eddies modify turbulence in the atmospheric boundary layer. In the case of cyclonic eddies, this modification triggers a slackening of near-surface winds, a decline in cloud fraction and water content, and a reduction in rainfall. We conclude that transient mesoscale ocean structures can significantly affect much larger atmospheric low-pressure systems that swiftly pass by at the latitudes investigated.

The zonal surface torque budget associated with the tropical wind stress anomalies during El Nino/Southern Oscillation is analyzed. Mountain and surface stress torques over South America are found to play a prominent role. Local momentum change is negligible for 6 month averages allowing the balance among regional contributions to the torque anomalies to be compared. During El Nino, eastward torque anomalies over the central equatorial Pacific are largely compensated by westward anomalies elsewhere in the equatorial band, notably over South America. Torque anomalies over South America and the Pacific in latitude bands north and south of the equator are both westward and are not compensated within the band, implying an export of eastward momentum to higher latitudes.

Mesoscale eddies are ubiquitous features in the Southern Ocean, yet their phenomenology is not well quantified. To tackle this task, we use satellite observations of sea level anomalies and sea surface temperature (SST) as well as in situ temperature and salinity measurements from profiling floats. Over the period 1997–2010, we identified over a million mesoscale eddy instances and were able to track about 105 of them over 1 month or more. The Antarctic Circumpolar Current (ACC), the boundary current systems, and the regions where they interact are hot spots of eddy presence, representing also the birth places and graveyards of most eddies. These hot spots contrast strongly to areas shallower than about 2000 m, where mesoscale eddies are essentially absent, likely due to topographical steering. Anticyclones tend to dominate the southern subtropical gyres, and cyclones the northern flank of the ACC. Major causes of regional polarity dominance are larger formation numbers and lifespans, with a contribution of differential propagation pathways of long-lived eddies. Areas of dominance of one polarity are generally congruent with the same polarity being longer-lived, bigger, of larger amplitude, and more intense. Eddies extend down to at least 2000 m. In the ACC, eddies show near surface temperature and salinity maxima, whereas eddies in the subtropical areas generally have deeper anomaly maxima, presumably inherited from their origin in the boundary currents. The temperature and salinity signatures of the average eddy suggest that their tracer anomalies are a result of both trapping in the eddy core and stirring.

Standing internal waves, so-called seiches, are ubiquitous in reservoirs and lakes. Although the stratification in such basin is often continuous, the modeling of seiches has been confined mostly to two-layer models. Such models are unable to give reliable insights into the vertical structure of the seiches, which might be crucial for the understanding of vertical mixing in natural water basins. To obtain this kind of information a two-dimensional computer model has been developed, which takes both continuous stratification and bottom topography into account. The results of this model are presented. The computed seiche modes reveal that (1) several large-scale modes can exist with similar eigenfrequencies, (2) the modes have a tendency to develop narrow jets and (3) only the lowest modes are strongly influenced by the bottom topography.

We analyze the linearized version of an analytical model, which combines linear ocean dynamics with a simple version of the Bjerknes hypothesis for El Nino. The ocean is represented by linear shallow water equations on an equatorial beta-plane. It is driven by zonal wind stress, which is assumed to have a fixed spatial form. Stress amplitude is set to be proportional to the thermocline displacement at the eastern boundary. It is shown that, for physically plausible parameter values, the model system can sustain growing Oscillations. Both growth rate and period scale directly with the time that an oceanic Kelvin wave needs to crow the basin. They are quite sensitive to the coupling parameter between thermocline displacement and wind stress, and the zonal location and meridional width of the wind. The most important parameter determining this behavior of the system is the coupling constant. For strong coupling the system exhibits exponential growth without oscillation. As the coupling is decreased ...

[1] In late boreal spring, especially May, a strong relationship exists in observations among precipitation anomalies over equatorial South America and the Atlantic intertropical convergence zone (ITCZ), and eastern equatorial Pacific and central equatorial Atlantic sea surface temperature anomalies (SSTA). A chain of correlations of equatorial Pacific SSTA, western equatorial Atlantic wind stress (WEA), equatorial Atlantic SSTA, sea surface height, and precipitation supports a causal chain in which El Nino/Southern Oscillation (ENSO) induces WEA stress anomalies, which in turn affect Atlantic equatorial ocean dynamics. These correlations show strong seasonality, apparently arising within the atmospheric links of the chain. This pathway and the influence of equatorial Atlantic SSTA on South American rainfall in May appear independent of that of the northern tropical Atlantic. Brazil's Nordeste is affected by the northern tropical Atlantic. The equatorial influence lies further to the north over the eastern Amazon and the Guiana Highlands.