ALBERT

Description: Changes in the background climate are known to affect El Niño–Southern Oscillation (ENSO) by altering feedbacks that control ENSO’s characteristics. Here, the sensitivity of ENSO variability to the background climate is investigated by utilizing two Community Earth System Model, version 1 (CESM1), simulations in which the solar constant is altered by ±25 W m−2. The resulting stable warm and cold climate mean state simulations differ in terms of ENSO amplitude, frequency, diversity, asymmetry, and seasonality. In the warm run, ENSO reveals a larger amplitude and occurs at higher frequencies relative to the cold and control runs as well as observations. The warm run also features more eastern Pacific El Niños, an increased asymmetry, and a stronger seasonal phase locking. These changes are linked to changes in the mean state via the amplifying and damping feedbacks. In the warm run, a shallower mean thermocline results in a stronger subsurface–surface coupling, whereas the cold run reveals reduced ENSO variability due to a reduced Bjerknes feedback in accordance with a deeper mean thermocline and enhanced surface wind stress. A strong zonal advective and upwelling feedback further contribute to the large ENSO amplitude in the run with a warmer mean state. In the cold run, ENSO events are partly forced by anomalous shortwave radiation. However, in light of the large temperature contrast between the simulations of up to 6 K in the tropical Pacific, the relatively small changes in ENSO variability highlight the robustness of ENSO dynamics under vastly different climate mean states.

Description: Two decades of high-resolution satellite observations and climate modeling studies have indicated strong ocean–atmosphere coupled feedback mediated by ocean mesoscale processes, including semipermanent and meandrous SST fronts, mesoscale eddies, and filaments. The air–sea exchanges in latent heat, sensible heat, momentum, and carbon dioxide associated with this so-called mesoscale air–sea interaction are robust near the major western boundary currents, Southern Ocean fronts, and equatorial and coastal upwelling zones, but they are also ubiquitous over the global oceans wherever ocean mesoscale processes are active. Current theories, informed by rapidly advancing observational and modeling capabilities, have established the importance of mesoscale and frontal-scale air–sea interaction processes for understanding large-scale ocean circulation, biogeochemistry, and weather and climate variability. However, numerous challenges remain to accurately diagnose, observe, and simulate mesoscale air–sea interaction to quantify its impacts on large-scale processes. This article provides a comprehensive review of key aspects pertinent to mesoscale air–sea interaction, synthesizes current understanding with remaining gaps and uncertainties, and provides recommendations on theoretical, observational, and modeling strategies for future air–sea interaction research.

Description: Several years of moored turbulence measurements from xpods at three sites in the equatorial cold tongues of Atlantic and Pacific Oceans yield new insights into proxy estimates of turbulence that specifically target the cold tongues. They also reveal previously unknown wind dependencies of diurnally varying turbulence in the near-critical stratified shear layers beneath the mixed layer and above the core of the Equatorial Undercurrent that we have come to understand as deep cycle (DC) turbulence. Isolated by the mixed layer above, the DC layer is only indirectly linked to surface forcing. Yet, it varies diurnally in concert with daily changes in heating/cooling. Diurnal composites computed from 10-min averaged data at fixed xpod depths show that transitions from daytime to nighttime mixing regimes are increasingly delayed with weakening wind stress t. These transitions are also delayed with respect to depth such that they follow a descent rate of roughly 6 m h-1, independent of t. We hypothesize that this wind-dependent delay is a direct result of wind-dependent diurnal warm layer deepening, which acts as the trigger to DC layer instability by bringing shear from the surface down-ward but at rates much slower than 6 m h-1. This delay in initiation of DC layer instability contributes to a reduction in daily averaged values of turbulence dissipation. Both the absence of descending turbulence in the sheared DC layer prior to arrival of the diurnal warm layer shear and the magnitude of the subsequent descent rate after arrival are roughly predicted by laboratory experiments on entrainment in stratified shear flows.

Description: Numerical weather prediction models operate on grid spacings of a few kilometers, where deep convection begins to become resolvable. Around this scale, the emergence of coherent structures in the planetary boundary layer, often hypothesized to be caused by cold pools, forces the transition from shallow to deep convection. Yet, the kilometer-scale range is typically not resolved by standard surface operational measurement networks. The measurement campaign FESSTVaL aimed at addressing this gap by observing atmospheric variability at the hectometer to kilometer scale, with a particular emphasis on cold pools, wind gusts and coherent patterns in the planetary boundary layer during summer. A unique feature was the distribution of 150 self-developed and low-cost instruments. More specifically, FESSTVaL included dense networks of 80 autonomous cold pool loggers, 19 weather stations and 83 soil sensor systems, all installed in a rural region of 15-km radius in eastern Germany, as well as self-developed weather stations handed out to citizens. Boundary layer and upper air observations were provided by 8 Doppler lidars and 4 microwave radiometers distributed at 3 supersites; water vapor and temperature were also measured by advanced lidar systems and an infrared spectrometer; and rain was observed by a X-band radar. An uncrewed aircraft, multicopters and a small radiometer network carried out additional measurements during a four-week period. In this paper, we present FESSTVaL’s measurement strategy and show first observational results including unprecedented highly-resolved spatio-temporal cold-pool structures, both in the horizontal as well as in the vertical dimension, associated with overpassing convective systems.

Description: As an important external forcing, the effect of the 11-yr solar cycle on the tropical Pacific decadal variability is an interesting question. Here, we systematically investigate the phase-locking of the atmosphere and ocean covariations to the solar cycle in the tropical Pacific and propose a new mechanism to explain these decadal covariations. In both observation/reanalysis datasets and a solar cycle forced sensitivity experiment (named the SOL experiment), the ocean heat content anomalies (OHCa; 300 m) resemble a La Niña–like pattern in the solar cycle ascending phase, and the Walker circulation shifts westward. In the declining phase, the opposite is true. The accumulative solar irradiation directly contributes to this coherent decadal variability via changing the warm water volume and the solar-related heat is redistributed by the ocean dynamic processes. During the 11-yr solar cycle, the Pacific Walker circulation anomalies maintain the OHCa in the western equatorial Pacific and work as negative feedback for the eastern Pacific to help the OHCa phase transition. In addition, oceanic meridional heat transport via the subtropical cells and the propagation of off-equatorial Rossby waves also provide a lagged negative feedback to the OHCa phase transition according to the 11-yr solar cycle. The decadal coupled responses of the tropical Pacific climate system are 2 years more lag in the SOL experiment than in the observation/reanalysis. Significance Statement Here, we propose a new mechanism that the heating effect of the accumulative solar irradiation during the 11-yr solar cycle can be “integrated” into the tropical Pacific OHC and then provide a bottom-up effect on the atmosphere at decadal time scales. The strongly coupled processes in this region amplify the decadal phase-locking of the covariations to the 11-yr solar cycle. Our study demonstrates the role of the 11-yr solar cycle in the tropical Pacific decadal variability and provides a new explanation for the “bottom-up” mechanism of the solar cycle forcing. Our results update the understanding of the tropical Pacific decadal variability and may help to improve climate predictions at decadal time scales.

Description: We investigate the origin of the equatorial Pacific cold sea surface temperature (SST) bias and its link to wind biases, local and remote, in the Kiel Climate Model (KCM). The cold bias is common in climate models participating in the 5 th and 6 th phases of the Coupled Model Intercomparison Project. In the coupled experiments with the KCM, the interannually varying NCEP/CFSR wind stress is prescribed over four spatial domains: globally, over the equatorial Pacific (EP), the northern Pacific (NP) and southern Pacific (SP). The corresponding EP SST bias is reduced by 100%, 52%, 12% and 23%, respectively. Thus, the EP SST bias is mainly attributed to the local wind bias, with small but not negligible contributions from the extratropical regions. Erroneous ocean circulation driven by overly strong winds cause the cold SST bias, while the surface-heat flux counteracts it. Extratropical Pacific SST biases contribute to the EP cold bias via the oceanic subtropical gyres, which is further enhanced by dynamical coupling in the equatorial region. The origin of the wind biases is examined by forcing the atmospheric component of the KCM in a stand-alone mode with observed SSTs and simulated SSTs from the coupled experiments. Wind biases over the EP, NP and SP regions originate in the atmosphere model. The cold EP SST bias substantially enhances the wind biases over all three regions, while the NP and SP SST biases support local amplification of the wind bias. This study suggests that improving surface-wind stress, at and off the equator, is a key to improve mean-state equatorial Pacific SST in climate models.

Description: NORP-SORP Workshop on Polar Fresh Water: Sources, Pathways and Impacts of Freshwater in Northern and Southern Polar Oceans and Seas (SPICE-UP)What: Up to 60 participants at a time and more than twice as many registrants in total from 20 nations and across experience levels met to discuss the current status of research on freshwater in both polar regions, future directions, and synergies between the Arctic and Southern Ocean research communitiesWhen: 19-21 September 2022 Where: Online

Description: This study utilizes observations and a series of idealized experiments to explore whether eastern Pacific (EP)- and central Pacific (CP)-type El Niño–Southern Oscillation (ENSO) events produce surface wind stress responses with distinct spatial structures. We find that the meridionally broader sea surface temperatures (SSTs) during CP events lead to zonal wind stresses that are also meridionally broader than those found during EP-type events, leading to differences in the near-equatorial wind stress curl. These wind spatial structure differences create differences in the associated pre- and post-ENSO event WWV response. For instance, the meridionally narrow winds found during EP events have (i) weaker wind stresses along 58N and 58S, leading to weaker Ekman-induced pre-event WWV changes; and (ii) stronger near-equatorial wind stress curls that lead to a much larger post-ENSO event WWV changes than during CP events. The latter suggests that, in the framework of the recharge oscillator model, the EP events have stronger coupling between sea surface temperatures (SST) and thermocline (WWV), supporting more clearly the phase transition of ENSO events, and therefore, the oscillating nature of ENSO than CP events. The results suggest that the spatial structure of the SST pattern and the related differences in the wind stress curl, are required along with equatorial wind stress to accurately model the WWV changes during EP- and CP-type ENSO events.

Description: Equatorial deep jets (EDJ) are zonal currents along the equator in all three ocean basins that alternate in direction with depth and time. In the Atlantic below the thermocline, they are the dominant variability on interannual timescales. Observations of equatorial deep jets are available but scarce, given the EDJs’ location at depth, their small vertical scale and their long periodicity of several years. In the last few years, Argo floats have added a significant amount of measurements at intermediate depth. In this study we therefore revise estimates of the EDJ scales based on Argo float data. Mostly, we use velocity data at 1000 m depth calculated from float displacement, which yield robust estimates of the Atlantic EDJ period (4.6 years), amplitude distribution, phase distribution, zonal wavelength (146.7°), and meridional structure. We also show that the equatorial amplitude of the EDJs’ first meridional mode Rossby wave component (9.8 cm s −1 ) is larger than that of their Kelvin wave component (2.8 cm s −1 ). Additionally, we present a new estimation of the EDJs’ vertical structure throughout the Atlantic basin, based on an equatorial geostrophic velocity reconstruction from hydrographic Argo float measurements from depths between 400 and 2000 m. Our new estimates from Argo float data provide the first basin-wide assessment of the Atlantic EDJ scales, as well as having smaller uncertainties than estimates from earlier studies.

Description: The physical processes driving the genesis of surface- and subsurface-intensified cyclonic and anticyclonic eddies originating from the coastal current system of the Mauritanian Upwelling Region are investigated using a high-resolution (~1.5 km) configuration of GFDL’s Modular Ocean Model. Estimating an energy budget for the boundary current reveals a baroclinically unstable state during its intensification phase in boreal summer and which is driving eddy generation within the near-coastal region. The mean poleward coastal flow’s interaction with the sloping topography induces enhanced anticyclonic vorticity, with potential vorticity close to zero generated in the bottom boundary layer. Flow separation at sharp topographic bends intensifies the anticyclonic vorticity, and submesoscale structures of low PV coalesce to form anticyclonic vortices. A combination of offshore Ekman transport and horizontal advection determined the amount of SACW in an anticyclonic eddy. A vortex with a relatively dense and low PV core will form an anticyclonic mode-water eddy, which will subduct along isopycnals while propagating offshore and hence be shielded from surface buoyancy forcing. Less contribution of dense SACW promotes the generation of surface anticyclonic eddies as the core is composed of a lighter water mass, which causes the eddy to stay closer to the surface and hence be exposed to surface buoyancy forcing. Simulated cyclonic eddies are formed between the rotational flow of an offshore anticyclonic vortex and a poleward flowing boundary current, with eddy potential energy being the dominant source of eddy kinetic energy. All three types of eddies play a key role in the exchange between the Mauritanian Coastal currents system and the adjacent eastern boundary shadow zone region.

Description: The Earth system is accumulating energy due to human-induced activities. More than 90% of this energy has been stored in the ocean as heat since 1970, with similar to 60% of that in the upper 700 m. Differences in upper-ocean heat content anomaly (OHCA) estimates, however, exist. Here, we use a dataset protocol for 1970-2008-with six instrumental bias adjustments applied to expendable bathythermograph (XBT) data, and mapped by six research groups-to evaluate the spatiotemporal spread in upper OHCA estimates arising from two choices: 1) those arising from instrumental bias adjustments and 2) those arising from mathematical (i.e., mapping) techniques to interpolate and extrapolate data in space and time. We also examined the effect of a common ocean mask, which reveals that exclusion of shallow seas can reduce global OHCA estimates up to 13%. Spread due to mapping method is largest in the Indian Ocean and in the eddy-rich and frontal regions of all basins. Spread due to XBT bias adjustment is largest in the Pacific Ocean within 30 degrees N-30 degrees S. In both mapping and XBT cases, spread is higher for 1990-2004. Statistically different trends among mapping methods are found not only in the poorly observed Southern Ocean but also in the well-observed northwest Atlantic. Our results cannot determine the best mapping or bias adjustment schemes, but they identify where important sensitivities exist, and thus where further understanding will help to refine OHCA estimates. These results highlight the need for further coordinated OHCA studies to evaluate the performance of existing mapping methods along with comprehensive assessment of uncertainty estimates.

Description: Modular Observation Solutions of Earth Systems (MOSES) is a novel observation system that is specifically designed to unravel the impact of distinct, dynamic events on the long-term development of environmental systems. Hydrometeorological extremes such as the recent European droughts or the floods of 2013 caused severe and lasting environmental damage. Modeling studies suggest that abrupt permafrost thaw events accelerate Arctic greenhouse gas emissions. Short-lived ocean eddies seem to comprise a significant share of the marine carbon uptake or release. Although there is increasing evidence that such dynamic events bear the potential for major environmental impacts, our knowledge on the processes they trigger is still very limited. MOSES aims at capturing such events, from their formation to their end, with high spatial and temporal resolution. As such, the observation system extends and complements existing national and international observation networks, which are mostly designed for long-term monitoring. Several German Helmholtz Association centers have developed this research facility as a mobile and modular “system of systems” to record energy, water, greenhouse gas, and nutrient cycles on the land surface, in coastal regions, in the ocean, in polar regions, and in the atmosphere—but especially the interactions between the Earth compartments. During the implementation period (2017–21), the measuring systems were put into operation and test campaigns were performed to establish event-driven campaign routines. With MOSES’s regular operation starting in 2022, the observation system will then be ready for cross-compartment and cross-discipline research on the environmental impacts of dynamic events.

Description: Since 1750, land use change and fossil fuel combustion has led to a 46 % increase in the atmospheric carbon dioxide (CO2) concentrations, causing global warming with substantial societal consequences. The Paris Agreement aims to limiting global temperature increases to well below 2°C above pre-industrial levels. Increasing levels of CO2 and other greenhouse gases (GHGs), such as methane (CH4) and nitrous oxide (N2O), in the atmosphere are the primary cause of climate change. Approximately half of the carbon emissions to the atmosphere is sequestered by ocean and land sinks, leading to ocean acidification but also slowing the rate of global warming. However, there are significant uncertainties in the future global warming scenarios due to uncertainties in the size, nature and stability of these sinks. Quantifying and monitoring the size and timing of natural sinks and the impact of climate change on ecosystems are important information to guide policy-makers’ decisions and strategies on reductions in emissions. Continuous, long-term observations are required to quantify GHG emissions, sinks, and their impacts on Earth systems. The Integrated Carbon Observation System (ICOS) was designed as the European in situ observation and information system to support science and society in their efforts to mitigate climate change. It provides standardized and open data currently from over 140 measurement stations across 12 European countries. The stations observe GHG concentrations in the atmosphere and carbon and GHG fluxes between the atmosphere, land surface and the oceans. This article describes how ICOS fulfills its mission to harmonize these observations, ensure the related long-term financial commitments, provide easy access to well-documented and reproducible high-quality data and related protocols and tools for scientific studies, and deliver information and GHG-related products to stakeholders in society and policy.

Description: In the equatorial Atlantic Ocean, meridional velocity variability exhibits a pronounced peak on intraseasonal timescales whereas zonal velocity dominantly varies on seasonal to interannual timescales. We focus on the intraseasonal meridional velocity variability away from the near-surface layer, its source regions and its pathways into the deep ocean. This deep intraseasonal velocity variability plays a key role in equatorial dynamics as it is an important energy source for the deep equatorial circulation. The results are based on the output of a high-resolution ocean model revealing intraseasonal energy levels along the equator at all depths that are in good agreement with shipboard and moored velocity data. Spectral analyses reveal a pronounced signal of intraseasonal Yanai waves with westward phase velocities and zonal wavelengths longer than 450 km. Different sources and characteristics of these Yanai waves are identified: near the surface between 40°W and 10°W low-baroclinic-mode Yanai waves with periods of around 30 days are exited. These waves have a strong seasonal cycle with a maximum in August. High-frequency Yanai waves (10–20-day period) are excited at the surface east of 10°W. In the region between the North Brazil Current and the Equatorial Undercurrent high-baroclinic-mode Yanai waves with periods between 30 and 40 days are generated. Yanai waves with longer periods (40-80 days) are shed from the Deep Western Boundary Current. The Yanai wave energy is carried along beams east- and downward thus explaining differences in strength, structure and periodicity of the meridional intraseasonal variability in the equatorial Atlantic Ocean.

Description: Marine heatwaves along the coast ofWestern Australia, referred to as Ningaloo Niño, have had dramatic impacts on the ecosystem in the recent decade. A number of local and remote forcing mechanisms have been put forward, however little is known about the depth structure of such temperature extremes. Utilizing an eddy-active global Ocean General Circulation Model, Ningaloo Niño and the corresponding cold Ningaloo Niña events are investigated between 1958-2016, with focus on their depth structure. The relative roles of buoyancy and wind forcing are inferred from sensitivity experiments. Composites reveal a strong symmetry between cold and warm events in their vertical structure and associated large-scale spatial patterns. Temperature anomalies are largest at the surface, where buoyancy forcing is dominant and extend down to 300m depth (or deeper), with wind forcing being the main driver. Large-scale subsurface anomalies arise from a vertical modulation of the thermocline, extending from the western Pacific into the tropical eastern Indian Ocean. The strongest Ningaloo Niños in 2000 and 2011 are unprecedented compound events, where long-lasting high temperatures are accompanied by extreme freshening, which emerges in association with La Niñas, more common and persistent during the negative phase of the Interdecadal Pacific Oscillation. It is shown that Ningaloo Niños during La Nina phases have a distinctively deeper reach and are associated with a strengthening of the Leeuwin Current, while events during El Niño are limited to the surface layer temperatures, likely driven by local atmosphere-ocean feedbacks, without a clear imprint on salinity and velocity.

Description: The Antarctic Slope Front (ASF) is a fundamental feature of the subpolar Southern Ocean that is still poorly observed. In this study we build a statistical climatology of the temperature and salinity fields of the upper 380 m of the Antarctic margin. We use a comprehensive compilation of observational datasets including the profiles gathered by instrumented marine mammals. The mapping method consists first of a decomposition in vertical modes of the combined temperature and salinity profiles. Then the resulting principal components are optimally interpolated on a regular grid and the monthly climatological profiles are reconstructed, providing a physically plausible representation of the ocean. The ASF is located with a contour method and a gradient method applied on the temperature field, two complementary approaches that provide a complete view of the ASF structure. The front extends from the Amundsen Sea to the eastern Weddell Sea and closely tracks the continental shelf break. It is associated with a sharp temperature gradient that is stronger in winter and weaker in summer. The emergence of the front in the Amundsen and Bellingshausen sectors appears to be seasonally variable (slightly more westward in winter than in summer). Investigation of the density gradients across the shelf break indicates a winter slowdown of the baroclinic component of the Antarctic Slope Current at the near surface, in contrast with the seasonal variability of the temperature gradient.

Description: There is a controversy about the nature of multidecadal climate variability in the North Atlantic (NA) region, concerning the roles of ocean circulation and atmosphere–ocean coupling. Here we describe NA multidecadal variability from a version of the Kiel Climate Model, in which both subpolar gyre (SPG)–Atlantic meridional overturning circulation (AMOC) coupling and atmosphere–ocean coupling are essential. The oceanic barotropic and meridional overturning streamfunctions and the sea level pressure are jointly analyzed to derive the leading mode of Atlantic sector variability. This mode accounting for 23.7% of the total combined variance is oscillatory with an irregular periodicity of 25–50 years and an e-folding time of about a decade. SPG and AMOC mutually influence each other and together provide the delayed negative feedback necessary for maintaining the oscillation. An anomalously strong SPG, for example, drives higher surface salinity and density in the NA’s sinking region. In response, oceanic deep convection and AMOC intensify, which, with a time delay of about a decade, reduces SPG strength by enhancing upper-ocean heat content. The weaker gyre leads to lower surface salinity and density in the sinking region, which reduces deep convection and eventually AMOC strength. There is a positive ocean–atmosphere feedback between the sea surface temperature and low-level atmospheric circulation over the southern Greenland area, with related wind stress changes reinforcing SPG changes, thereby maintaining the (damped) multidecadal oscillation against dissipation. Stochastic surface heat flux forcing associated with the North Atlantic Oscillation drives the eigenmode.

Description: The Agulhas Current (AC) creates a sharp temperature gradient with the surrounding ocean, leading to a large turbulent flux of moisture from ocean to atmosphere. We use two simulations of the Weather Research and Forecasting (WRF) model to show the seasonal impact of the warm core of the AC on southern Africa precipitation. In one simulation the sea surface temperature (SST) of the AC is similar to satellite observations, while the second uses satellite SST observations spatially smoothed to reduce the temperature of the core of the AC by ~1.5°C. We show that decreasing the SST of the AC reduces the precipitation of the wettest seasons (austral summer and autumn) inland. Over the ocean, reducing the SST reduces precipitation, low-level wind convergence, SST and SLP Laplacian above the AC in all seasons, consistent with the pressure adjustment mechanism. Moreover, winter precipitation above the Current may be also related to increased latent flux. In summer and autumn, the AC SST reduction is also associated with decreased precipitation further inland (more than 1.5 mm/day), caused by an atmospheric circulation that decreases the horizontal moisture flux from the AC to South Africa. The reduction is also associated with higher geopotential height extending from the surface east and over the AC to the mid-troposphere over southeastern Africa. The westward tilted geopotential height is consistent with the linear response to shallow diabatic heating in midlatitudes. An identical mechanism occurs in spring but is weaker. Winter rainfall response is confined above the AC.

Description: Spatial and temporal variations of nutrient-rich upwelled water across the major eastern boundary upwelling systems are primarily controlled by the surface wind with different, and sometimes contrasting, impacts on coastal upwelling systems driven by alongshore wind and offshore upwelling systems driven by the local wind-stress-curl. Here, concurrently measured wind-fields, satellite-derived Chlorophyll-a concentration along with a state-of-the-art ocean model simulation spanning 2008-2018 are used to investigate the connection between coastal and offshore physical drivers of the Benguela Upwelling System (BUS). Our results indicate that the spatial structure of long-term mean upwelling derived from Ekman theory and the numerical model are fairly consistent across the entire BUS and closely followed by the Chlorophyll-a pattern. The variability of the upwelling from the Ekman theory is proportionally diminished with offshore distance, whereas different and sometimes opposite structures are revealed in the model-derived upwelling. Our result suggests the presence of sub-mesoscale activity (i.e., filaments and eddies) across the entire BUS with a large modulating effect on the wind-stress-curl-driven upwelling off Lüderitz and Walvis Bay. In Kunene and Cape Frio upwelling cells, located in the northern sector of the BUS, the coastal upwelling and open-ocean upwelling frequently alternate each other, whereas they are modulated by the annual cycle and mostly in phase off Walvis Bay. Such a phase relationship appears to be strongly seasonally dependent off Lüderitz and across the southern BUS. Thus, our findings suggest this relationship is far more complex than currently thought and seems to be sensitive to climate changes with short- and far-reaching consequences for this vulnerable marine ecosystem.

Description: Enhanced Southern Ocean ventilation in recent decades has been suggested to be a relevant modulator of the observed changes in ocean heat and carbon uptake. This study focuses on the Southern Ocean midlatitude ventilation changes from the 1960s to the 2010s. A global 1/4° configuration of the NEMO–Louvain-la-Neuve sea ice model, version 2 (LIM2), including the inert tracer CFC-12 (a proxy of ocean ventilation) is forced with the CORE, phase II (CORE-II), and JRA-55 driving ocean (JRA55-do) atmospheric reanalyses. Sensitivity experiments, where the variability of wind stress and/or the buoyancy forcing is suppressed on interannual time scales, are used to unravel the mechanisms driving ventilation changes. Ventilation changes are estimated by comparing CFC-12 interior inventories among the different experiments. All simulations suggest a multidecadal fluctuation of Southern Ocean ventilation, with a decrease until the 1980s–90s and a subsequent increase. This evolution is related to the atmospheric forcing and is caused by the (often counteracting) effects of wind stress and buoyancy forcing. Until the 1980s, increased buoyancy gains caused the ventilation decrease, whereas the subsequent ventilation increase was driven by strengthened wind stress causing deeper mixed layers and a stronger meridional overturning circulation. Wind stress emerges as the main driver of ventilation changes, even though buoyancy forcing modulates its trend and decadal variability. The three Southern Ocean basins take up CFC-12 in distinct density intervals but overall respond similarly to the atmospheric forcing. This study suggests that Southern Ocean ventilation is expected to increase as long as the effect of increasing Southern Hemisphere wind stress overwhelms that of increased stratification.

Description: The cold-water coral Lophelia pertusa builds up bioherms that sustain high biodiversity in the deep ocean worldwide. Photographic monitoring of the polyp activity represents a helpful tool to characterize the health status of the corals and to assess anthropogenic impacts on the microhabitat. Discriminating active polyps from skeletons of white Lophelia pertusa is usually time-consuming and error-prone due to their similarity in color in common RGB camera footage. Acquisition of finer resolved spectral information might increase the contrast between the segments of polyps and skeletons, and therefore could support automated classification and accurate activity estimation of polyps. For recording the needed footage, underwater multispectral imaging systems can be used, but they are often expensive and bulky. Here we present results of a new, light-weight, compact and low-cost deep-sea tunable LED-based underwater multispectral imaging system (TuLUMIS) with eight spectral channels. A brunch of healthy white Lophelia pertusa was observed under controlled conditions in a laboratory tank. Spectral reflectance signatures were extracted from pixels of polyps and skeletons of the observed coral. Results showed that the polyps can be better distinguished from the skeleton by analysis of the eight-dimensional spectral reflectance signatures compared to three-channel RGB data. During a 72-hour monitoring of the coral with a half-hour temporal resolution in the lab, the polyp activity was estimated based on the results of the multispectral pixel classification using a support vector machine (SVM) approach. The computational estimated polyp activity was consistent with that of the manual annotation, which yielded a correlation coefficient of 0.957.

Description: The El Niño-Southern Oscillation (ENSO) is the dominant mode of interannual climate variability on the planet, with far-reaching global impacts. It is therefore key to evaluate ENSO simulations in state-of-the-art numerical models used to study past, present and future climate. Recently, the Pacific Region Panel of the International Climate and Ocean - Variability, Predictability, and Change (CLIVAR) Project, as a part of the World Climate Research Programme (WCRP), led a community-wide effort to evaluate the simulation of ENSO variability, teleconnections and processes in climate models. The new CLIVAR 2020 ENSO metrics package enables model diagnosis, comparison, and evaluation to (1) highlight aspects that need improvement; (2) monitor progress across model generations; (3) help in selecting models that are well suited for particular analyses; (4) reveal links between various model biases, illuminating the impacts of those biases on ENSO and its sensitivity to climate change; and to (5) advance ENSO literacy. By interfacing with existing model evaluation tools, the ENSO metrics package enables rapid analysis of multi-petabyte databases of simulations, such as those generated by the Coupled Model Intercomparison Project phases 5 (CMIP5) and 6 (CMIP6). The CMIP6 models are found to significantly outperform those from CMIP5 for 8 out of 24 ENSO-relevant metrics, with most CMIP6 models showing improved tropical Pacific seasonality and ENSO teleconnections. Only one ENSO metric is significantly degraded in CMIP6, namely the coupling between the ocean surface and subsurface temperature anomalies, while the majority of metrics remain unchanged.

Description: This study demonstrates that the generalization that strong anomalous equatorial Pacific westerly (easterly) winds during El Niño (La Niña) events displays strong adjusted warm water volume (WWV) discharges (recharges) is often incorrect. Using ocean model simulations, we categorize the oceanic adjusted responses to strong anomalous equatorial winds into two categories: (i) transitioning (consistent with the above generalization); and (ii) neutral adjusted responses (with negligible WWV re- and discharge) During the 1980-2016 period only 47% of strong anomalous equatorial winds are followed by transitioning adjusted responses, while the remaining are followed by neutral adjusted responses. Moreover, 55% (only 30%) of the strongest winds lead to transitioning adjusted responses during the pre-2000 (post-2000) period in agreement with the previously reported post-2000 decline of WWV lead time to El Niño-Southern Oscillation (ENSO) events. The prominent neutral adjusted WWV response is shown to be largely excited by anomalous wind stress forcing with a weaker curl (on average consistent with a higher ratio of off-equatorial to equatorial wind events) and weaker Rossby wave projection than the transitioning adjusted response. We also identify a prominent ENSO phase asymmetry where strong anomalous equatorial westerly winds (i.e., El Niño events) are roughly 1.6 times more likely to strongly discharge WWV than strong anomalous equatorial easterly winds (i.e., La Niña events) are to strongly recharge WWV. This ENSO phase asymmetry may be added to the list of mechanisms proposed to explain why El Niño events have a stronger tendency to be followed by La Niña events than vice versa.

Description: The extratropical effect of the quasi-biennial oscillation (QBO), known as the Holton-Tan effect, is manifest as a weaker, warmer winter Arctic polar vortex during the east QBO phase. While previous studies have shown that the extratropical QBO signal is caused by the modified propagation of planetary waves in the stratosphere, the mechanism dominating the onset and seasonal development of the Holton-Tan effects remains unclear. Here, the governing wave-mean flow dynamics of the early winter extratropical QBO signal onset and its reversibility is investigated on a synoptic time scale with a finite-amplitude diagnostic using reanalysis and a chemistry-climate model. The extratropical QBO signal onset in October is found to primarily result from modulated stratospheric life cycles of wave pulses entering the stratosphere from the troposphere, rather than from a modulation of their tropospheric wave source. A comprehensive analysis of the wave activity budget during fall, when the stratospheric winter polar vortex starts forming and waves start propagating up into the stratosphere, shows significant differences. During the east QBO phase, the deceleration of the mid-high-latitude stratospheric zonal-mean jet by the upward-propagating wave pulses is less reversible, due to stronger dissipation processes, while during the west phase, a more reversible deceleration of the main polar vortex is found owing to the waves being dissipated at lower latitudes, accompanied by a weak but different response of the tropospheric subtropical jet. From this synoptic wave-event viewpoint, the early season onset of the Holton-Tan effect results from the cumulative effect of the QBO dependent wave-induced deceleration during the life cycle of individual upward wave pulses.

Description: The representation of tropical precipitation is evaluated across three generations of models participating in phases 3, 5, and 6 of the Coupled Model Intercomparison Project (CMIP). Compared to state-of-the-art observations, improvements in tropical precipitation in the CMIP6 models are identified for some metrics, but we find no general improvement in tropical precipitation on different temporal and spatial scales. Our results indicate overall little changes across the CMIP phases for the summer monsoons, the double-ITCZ bias, and the diurnal cycle of tropical precipitation. We find a reduced amount of drizzle events in CMIP6, but tropical precipitation occurs still too frequently. Continuous improvements across the CMIP phases are identified for the number of consecutive dry days, for the representation of modes of variability, namely, the Madden–Julian oscillation and El Niño–Southern Oscillation, and for the trends in dry months in the twentieth century. The observed positive trend in extreme wet months is, however, not captured by any of the CMIP phases, which simulate negative trends for extremely wet months in the twentieth century. The regional biases are larger than a climate change signal one hopes to use the models to identify. Given the pace of climate change as compared to the pace of model improvements to simulate tropical precipitation, we question the past strategy of the development of the present class of global climate models as the mainstay of the scientific response to climate change. We suggest the exploration of alternative approaches such as high-resolution storm-resolving models that can offer better prospects to inform us about how tropical precipitation might change with anthropogenic warming.

Description: Weather and climate variations on subseasonal to decadal time scales can have enormous social, economic, and environmental impacts, making skillful predictions on these time scales a valuable tool for decision-makers. As such, there is a growing interest in the scientific, operational, and applications communities in developing forecasts to improve our foreknowledge of extreme events. On subseasonal to seasonal (S2S) time scales, these include high-impact meteorological events such as tropical cyclones, extratropical storms, floods, droughts, and heat and cold waves. On seasonal to decadal (S2D) time scales, while the focus broadly remains similar (e.g., on precipitation, surface and upper-ocean temperatures, and their effects on the probabilities of high-impact meteorological events), understanding the roles of internal variability and externally forced variability such as anthropogenic warming in forecasts also becomes important. The S2S and S2D communities share common scientific and technical challenges. These include forecast initialization and ensemble generation; initialization shock and drift; understanding the onset of model systematic errors; bias correction, calibration, and forecast quality assessment; model resolution; atmosphere-ocean coupling; sources and expectations for predictability; and linking research, operational forecasting, and end-user needs. In September 2018 a coordinated pair of international conferences, framed by the above challenges, was organized jointly by the World Climate Research Programme (WCRP) and the World Weather Research Programme (WWRP). These conferences surveyed the state of S2S and S2D prediction, ongoing research, and future needs, providing an ideal basis for synthesizing current and emerging developments in these areas that promise to enhance future operational services. This article provides such a synthesis.

Description: There is a zonally oriented teleconnection pattern over the high-latitude Eurasian continent, which is maintained through baroclinic energy conversion. In this study, we investigate the unique features of the maintenance mechanism of this teleconnection. It is found that the baroclinic energy conversion is most efficient in both the mid-troposphere and the lower troposphere, and that the baroclinic energy conversion in the lower troposphere is comparable to that in the mid-troposphere. Further results indicate that the basic state plays a crucial role in the baroclinic energy conversion. For both the mid and lower troposphere, the atmospheric stability is low and the Coriolis parameter is large over high-latitude Eurasia, favoring strong baroclinic energy conversion. Particularly, in the lower troposphere, the atmospheric stability exhibits a clear land-sea contrast, favoring baroclinic energy conversion over the continents rather than the oceans. Furthermore, in the lower troposphere, the in-phase configuration of the meridional wind and temperature anomalies, which results from the strong meridional gradient of mean temperature around the north edge of the Eurasian continent, also significantly contributes to baroclinic energy conversion. This study highlights the role of the basic state of temperature rather than zonal wind in maintaining the high-latitude teleconnection through baroclinic energy conversion.

Description: Subtropical dry zones, located in the Hadley cells' subsidence regions, strongly influence regional climate as well as outgoing longwave radiation. Changes in these dry zones could have significant impact on surface climate as well as on the atmospheric energy budget. This study investigates the behavior of upper-tropospheric dry zones in a changing climate, using the variable upper-tropospheric humidity (UTH), calculated from climate model experiment output as well as from radiances measured with satellite-based sensors. The global UTH distribution shows that dry zones form a belt in the subtropical winter hemisphere. In the summer hemisphere they concentrate over the eastern ocean basins, where the descent regions of the subtropical anticyclones are located. Recent studies with model and satellite data have found tendencies of increasing dryness at the poleward edges of the subtropical subsidence zones. However, UTH calculated from climate simulations with 25 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) shows these tendencies only for parts of the winter-hemispheric dry belts. In the summer hemisphere, even though differences exist between the simulations, UTH is increasing in most dry zones, particularly in the South and North Pacific Ocean. None of the summer dry zones is expanding in these simulations. Upper-tropospheric dry zones estimated from observational data do not show any robust signs of change since 1979. Apart from a weak drying tendency at the poleward edge of the southern winter-hemispheric dry belt in infrared measurements, nothing indicates that the subtropical dry belts have expanded poleward.

Description: It might be impossible to truly fathom the magnitude of the threat that global-mean sea level rise poses. However, conceptualizing the scale of the solutions required to protect ourselves against global-mean sea level rise, aids in our ability to acknowledge and understand the threat that sea level rise poses. On these grounds, we here discuss a means to protect over 25 million people and important economical regions in northern Europe against sea level rise. We propose the construction of a Northern European Enclosure Dam (NEED) that stretches between France, the United Kingdom and Norway. NEED may seem an overwhelming and unrealistic solution at first. However, our preliminary study suggests that NEED is potentially favorable financially, but also in scale, impacts and challenges compared to that of alternative solutions, such as (managed) migrations and that of country-by-country protection efforts. The mere realization that a solution as considerable as NEED might be a viable and cost-effective protection measure is illustrative of the extraordinary global threat of global-mean sea level rise that we are facing. As such, the concept of constructing NEED showcases the extent of protection efforts that are required if mitigation efforts fail to limit sea level rise.

Description: The comparison of equivalent neutral winds obtained from (a) four WHOI buoys in the subtropics and (b) scatterometer estimates at those locations reveals a root-mean-square (RMS) difference of 0.56-0.76 m/s. To investigate this RMS difference, different buoy wind error sources were examined. These buoys are particularly well suited to examine two important sources of buoy wind errors because: (1) redundant anemometers and a comparison with numerical flow simulations allow us to quantitatively assess flow distortion errors, and (2) one-minute sampling at the buoys allows us to examine the sensitivity of buoy temporal sampling/averaging in the buoy-scatterometer comparisons. The inter-anemometer difference varies as a function of wind direction relative to the buoy wind vane and is consistent with the effects of flow distortion expected based on numerical flow simulations. Comparison between the anemometers and scatterometer winds supports the interpretation that the inter-anemometer disagreement, which can be up to 5% of the wind speed, is due to flow distortion. These insights motivate an empirical correction to the individual anemometer records and subsequent comparison with scatterometer estimates show good agreement.

Description: The North Atlantic (NA) basin-averaged sea surface temperature (NASST) is often used as an index to study climate variability in the NA sector. However, there is still some debate on what drives it. Based on observations and climate models, an analysis of the different influences on the NASST index and its low-pass filtered version, the Atlantic multidecadal oscillation (AMO) index, is provided. In particular, the relationships of the two indices with some of its mechanistic drivers including the Atlantic meridional overturning circulation (AMOC) are investigated. In observations, the NASST index accounts for significant SST variability over the tropical and subpolar NA. The NASST index is shown to lump together SST variability originating from different mechanisms operating on different time scales. The AMO index emphasizes the subpolar SST variability. In the climate models, the SST-anomaly pattern associated with the NASST index is similar. The AMO index, however, only represents pronounced SST variability over the extratropical NA, and this variability is significantly linked to the AMOC. There is a sensitivity of this linkage to the cold NA SST bias observed in many climate models. Models suffering from a large cold bias exhibit a relatively weak linkage between the AMOC and AMO and vice versa. Finally, the basin-averaged SST in its unfiltered form, which has been used to question a strong influence of ocean dynamics on NA SST variability, mixes together multiple types of variability occurring on different time scales and therefore underemphasizes the role of ocean dynamics in the multidecadal variability of NA SSTs.

Description: MILAN was a multidisciplinary, international study examining how the diel variability of sea-surface microlayer biogeochemical properties potentially impacts ocean-atmosphere interaction, in order to improve our understanding of this globally important process. The sea-surface microlayer (SML) at the air-sea interface is 〈 1 mm deep but it is physically, chemically and biologically distinct from the underlying water and the atmosphere above. Wind-driven turbulence and solar radiation are important drivers of SML physical and biogeochemical properties. Given that the SML is involved in all ocean-atmosphere exchanges of mass and energy, its response to solar radiation, especially in relation to how it regulates the air-sea exchange of climate-relevant gases and aerosols, is surprisingly poorly characterised. MILAN (sea-surface MIcroLAyer at Night) was an international, multidisciplinary campaign designed to specifically address this issue. In spring 2017, we deployed diverse sampling platforms (research vessels, radio-controlled catamaran, free-drifting buoy) to study full diel cycles in the coastal North Sea SML and in underlying water, and installed a land-based aerosol sampler. We also carried out concurrent ex situ experiments using several microsensors, a laboratory gas exchange tank, a solar simulator, and a sea spray simulation chamber. In this paper we outline the diversity of approaches employed and some initial results obtained during MILAN. Our observations of diel SML variability, e.g. the influence of changing solar radiation on the quantity and quality of organic material, and diel changes in wind intensity primarily forcing air-sea CO2 exchange, underline the value and the need of multidisciplinary campaigns for integrating SML complexity into the context of air-sea interaction.

Description: Mesoscale eddies can be strengthened by the absorption of submesoscale eddies resulting from mixed-layer baroclinic instabilities. This is shown for mesoscale eddies in the Agulhas Current system by investigating the kinetic energy cascade with a spectral and a coarse-graining approach in two model simulations of the Agulhas region. One simulation resolves mixed-layer baroclinic instabilities and one does not. When mixed-layer baroclinic instabilities are included, the largest submesoscale near-surface fluxes occur in winter-time in regions of strong mesoscale activity for upscale as well as downscale directions. The forward cascade at the smallest resolved scales occurs mainly in frontogenetic regions in the upper 30 m of the water column. In the Agulhas ring path, the forward cascade changes to an inverse cascade at a typical scale of mixed-layer eddies (15 km). At the same scale, the largest sources of the upscale flux occur. After the winter, the maximum of the upscale flux shifts to larger scales. Depending on the region, the kinetic energy reaches the mesoscales in spring or early summer aligned with the maximum of mesoscale kinetic energy. This indicates the importance of submesoscale flows for the mesoscale seasonal cycle. A case study shows that the underlying process is the mesoscale absorption of mixed-layer eddies. When mixed-layer baroclinic instabilities are not included in the simulation, the open-ocean upscale cascade in the Agulhas ring path is almost absent. This contributes to a 20 %-reduction of surface kinetic energy at mesoscales larger than 100 km when submesoscale dynamics are not resolved by the model.

Description: The structure, transport, and seasonal variability of the West Greenland boundary current system near Cape Farewell are investigated using a high-resolution mooring array deployed from 2014 to 2018. The boundary current system is comprised of three components: the West Greenland Coastal Current, which advects cold and fresh Upper Polar Water (UPW); the West Greenland Current, which transports warm and salty Irminger Water (IW) along the upper slope and UPW at the surface; and the Deep Western Boundary Current, which advects dense overflow waters. Labrador Sea Water (LSW) is prevalent at the seaward side of the array within an offshore recirculation gyre and at the base of the West Greenland Current. The 4-yr mean transport of the full boundary current system is 31.1 ± 7.4 Sv (1 Sv ≡ 106 m3 s-1), with no clear seasonal signal. However, the individual water mass components exhibit seasonal cycles in hydrographic properties and transport. LSW penetrates the boundary current locally, through entrainment/mixing from the adjacent re-circulation gyre, and also enters the current upstream in the Irminger Sea. IW is modified through air–sea interaction during winter along the length of its trajectory around the Irminger Sea, which converts some of the water to LSW. This, together with the seasonal increase in LSW entering the current, results in an anticorrelation in transport between these two water masses. The seasonality in UPW transport can be explained by remote wind forcing and subsequent adjustment via coastal trapped waves. Our results provide the first quantitatively robust observational description of the boundary current in the eastern Labrador Sea.

Description: State of the climate in 2019

Description: Marine phytoplankton blooms are annual spring events that sustain active and diverse bloom-associated bacterial populations. Blooms vary considerably in terms of eukaryotic species composition and environmental conditions, but a limited number of heterotrophic bacterial lineages — primarily members of the Flavobacteriia, Alphaproteobacteria and Gammaproteobacteria — dominate these communities. In this Review, we discuss the central role that these bacteria have in transforming phytoplankton-derived organic matter and thus in biogeochemical nutrient cycling. On the basis of selected field and laboratory-based studies of flavobacteria and roseobacters, distinct metabolic strategies are emerging for these archetypal phytoplankton-associated taxa, which provide insights into the underlying mechanisms that dictate their behaviours during blooms.

Description: The synthetic production of monodisperse single magnetic domain nanoparticles at ambient temperature is challenging. In nature, magnetosomes--membrane-bound magnetic nanocrystals with unprecedented magnetic properties--can be biomineralized by magnetotactic bacteria. However, these microbes are difficult to handle. Expression of the underlying biosynthetic pathway from these fastidious microorganisms within other organisms could therefore greatly expand their nanotechnological and biomedical applications. So far, this has been hindered by the structural and genetic complexity of the magnetosome organelle and insufficient knowledge of the biosynthetic functions involved. Here, we show that the ability to biomineralize highly ordered magnetic nanostructures can be transferred to a foreign recipient. Expression of a minimal set of genes from the magnetotactic bacterium Magnetospirillum gryphiswaldense resulted in magnetosome biosynthesis within the photosynthetic model organism Rhodospirillum rubrum. Our findings will enable the sustainable production of tailored magnetic nanostructures in biotechnologically relevant hosts and represent a step towards the endogenous magnetization of various organisms by synthetic biology.

Description: Marine phytoplankton blooms are annual spring events that sustain active and diverse bloom-associated bacterial populations. Blooms vary considerably in terms of eukaryotic species composition and environmental conditions, but a limited number of heterotrophic bacterial lineages — primarily members of the Flavobacteriia, Alphaproteobacteria and Gammaproteobacteria — dominate these communities. In this Review, we discuss the central role that these bacteria have in transforming phytoplankton-derived organic matter and thus in biogeochemical nutrient cycling. On the basis of selected field and laboratory-based studies of flavobacteria and roseobacters, distinct metabolic strategies are emerging for these archetypal phytoplankton-associated taxa, which provide insights into the underlying mechanisms that dictate their behaviours during blooms.

Description: In this study, the authors discuss two different parameterizations for the effect of mixed layer eddies, one based on ageostrophic linear stability analysis (ALS) and the other one based on a scaling of the potential energy release by eddies (PER). Both parameterizations contradict each other in two aspects. First, they predict different functional relationships between the magnitude of the eddy fluxes and the Richardson number (Ri) related to the background state. Second, they also predict different vertical structure functions for the horizontal eddy fluxes. Numerical simulations for two different configurations and for a large range of different background conditions are used to evaluate the parameterizations. It turns out that PER is better suited to capture the Ri dependency of the magnitude of the eddy fluxes. On the other hand, the vertical structure of the meridional eddy fluxes predicted by ALS is more accurate than that of PER, while the vertical structure of the vertical eddy fluxes is well predicted by both parameterizations. Therefore, this study suggests the use of the magnitude of PER and the vertical structure functions of ALS for an improved parameterization of mixed layer eddy fluxes.

Description: Northern Hemisphere stratospheric variability is investigated with respect to chaotic behavior using time series from three different variables extracted from four different reanalysis products and two numerical model runs with different forcing. The time series show red spectra at all frequencies and the probability distribution functions show persistent deviations from a Gaussian distribution. An exception is given by the numerical model forced with perpetual winter conditions—a case that shows more variability and follows a Gaussian distribution, suggesting that the deviation from Gaussianity found in the observations is due to the transition between summer and winter variability. To search for the presence of a chaotic attractor the correlation dimension and entropy, the Lyapunov spectrum, and the associated Kaplan–Yorke dimension are estimated. A finite value of the dimensions can be computed for each variable and data product, with the correlation dimension ranging between 3.0 and 4.0 and the Kaplan–Yorke dimension between 3.3 and 5.5. The correlation entropy varies between 0.6 and 1.1. The model runs show similar values for the correlation and Lyapunov dimensions for both the seasonally forced run and the perpetual-winter run, suggesting that the structure of a possible chaotic attractor is not determined by the seasonality in the forcing, but must be given by other mechanisms.

Description: Southern Hemisphere (SH) stratospheric variability is investigated with respect to chaotic behavior using time series from three different variables extracted from four different reanalysis products. The results are compared with the same analysis applied to the Northern Hemisphere (NH). The probability density functions (PDFs) for the SH show persistent deviations from a Gaussian distribution. The variability is given by white spectra for low frequencies, a slope of −1 for intermediate frequencies, and −3 slopes for high frequencies. Considering the time series for winter and summer separately, PDFs show a Gaussian distribution and the variability spectra change their slopes, indicating the role of the transition between winter and summer variability in shaping the time series. The correlation (D2) and the Kaplan–Yorke (DKY) dimensions are estimated. A finite value of the dimensions can be computed for each variable and data product, except for the NCEP zonal-mean zonal wind and temperature data, which violate the requirement D2 ≤ DKY, possibly owing to the presence of spurious trends and inconsistencies in the data. The value of D2 ranges between 2.6 and 3.9, while DKY ranges between 3.0 and 4.5. The results show that both D2 and DKY display large variability in their values both for different datasets and for different variables within the same dataset. The variability of the values of D2 and DKY thus leaves open the question about the existence of a low-dimensional attractor or if the finite dimensions of the system are the result of the projection of a larger attractor in a low-dimensional embedding space.

Description: The sensitivities of the Brewer–Dobson circulation (BDC) to different distributions of tropical SST heating are investigated in an idealized aquaplanet model. It is found that an increase in tropical SSTs generally leads to an acceleration of tropical upwelling and an associated reduction in the age of air (AOA) in the polar stratosphere and that the AOA near the subtropical tropopause is correlated with local isentropic mixing of tropospheric air with stratospheric air. The zonal distribution of SST perturbations has a major impact on the vertical and meridional structure of the BDC as compared with other SST characteristics. Zonally localized SST heatings tend to generate a shallow acceleration of the stratospheric residual circulation, enhanced isentropic mixing associated with a weakened stratospheric jet, and a reduction in AOA mostly within the polar vortex. In contrast, SST heatings with a zonally symmetric structure tend to produce a deep strengthening of the stratospheric residual circulation, suppressed isentropic mixing associated with a stronger stratospheric jet, and a decrease of AOA in the entire stratosphere. The shallow versus deep strengthening of the stratospheric residual circulation change has been linked to wave propagation and dissipation in the subtropical lower stratosphere rather than wave generation in the troposphere, and the former can be strongly affected by the vertical position of the subtropical jet. These results suggest that, while the longitudinally localized SST trends under climate change may contribute to the change in the shallow branch of the BDC, the upward shift of the subtropical jet associated with the zonal SST heating can impact the deep branch of the BDC.

Description: The authors test the hypothesis that recent observed trends in surface westerlies in the Southern Hemisphere are directly consequent on observed trends in the timing of stratospheric final warming events. The analysis begins by verifying that final warming events have an impact on tropospheric circulation in a simplified GCM driven by specified equilibrium temperature distributions. Seasonal variations are imposed in the stratosphere only. The model produces qualitatively realistic final warming events whose influence extends down to the surface, much like what has been reported in observational analyses. The authors then go on to study observed trends in surface westerlies composited with respect to the date of final warming events. If the considered hypothesis were correct, these trends would appear to be much weaker when composited with respect to the date of the final warming events. The authors find that this is not the case, and accordingly they conclude that the observed surface changes cannot be attributed simply to this shift toward later final warming events.

Description: Collectively, marine sediments comprise the largest reservoir of methane on Earth. The flux of methane from the sea bed to the overlying water column is mitigated by the sulphate-dependent anaerobic oxidation of methane by marine microbes within a discrete sedimentary horizon termed the sulphate–methane transition zone. According to conventional isotope systematics, the biological consumption of methane leaves a residue of methane enriched in 13C (refs 1, 2, 3). However, in many instances the methane within sulphate–methane transition zones is depleted in 13C, consistent with the production of methane, and interpreted as evidence for the intertwined anaerobic oxidation and production of methane4, 5, 6. Here, we report results from experiments in which we incubated cultures of microbial methane consumers with methane and low levels of sulphate, and monitored the stable isotope composition of the methane and dissolved inorganic carbon pools over time. Residual methane became progressively enriched in 13C at sulphate concentrations above 0.5 mM, and progressively depleted in 13C below this threshold. We attribute the shift to 13C depletion during the anaerobic oxidation of methane at low sulphate concentrations to the microbially mediated carbon isotope equilibration between methane and carbon dioxide. We suggest that this isotopic effect could help to explain the 13C-depletion of methane in subseafloor sulphate–methane transition zones.

Description: Mammalian organs are challenging to study as they are fairly inaccessible to experimental manipulation and optical observation. Recent advances in three-dimensional (3D) culture techniques, coupled with the ability to independently manipulate genetic and microenvironmental factors, have enabled the real-time study of mammalian tissues. These systems have been used to visualize the cellular basis of epithelial morphogenesis, to test the roles of specific genes in regulating cell behaviours within epithelial tissues and to elucidate the contribution of microenvironmental factors to normal and disease processes. Collectively, these novel models can be used to answer fundamental biological questions and generate replacement human tissues, and they enable testing of novel therapeutic approaches, often using patient-derived cells.

Description: Decadal climate variability has long received limited attention. With the slow-down in surface warming since the late 1990s, the decadal scale has rightly become a focus of attention: for assessing climate change and its impacts, it is of critical importance

Description: Changes in solar activity have previously been proposed to cause decadal- to millennial-scale fluctuations in both the modern and Holocene climates1. Direct observational records of solar activity, such as sunspot numbers, exist for only the past few hundred years, so solar variability for earlier periods is typically reconstructed from measurements of cosmogenic radionuclides such as 10Be and 14C from ice cores and tree rings2, 3. Here we present a high-resolution 10Be record from the ice core collected from central Greenland by the Greenland Ice Core Project (GRIP). The record spans from 22,500 to 10,000 years ago, and is based on new and compiled data4, 5, 6. Using 14C records7, 8 to control for climate-related influences on 10Be deposition, we reconstruct centennial changes in solar activity. We find that during the Last Glacial Maximum, solar minima correlate with more negative δ18O values of ice and are accompanied by increased snow accumulation and sea-salt input over central Greenland. We suggest that solar minima could have induced changes in the stratosphere that favour the development of high-pressure blocking systems located to the south of Greenland, as has been found in observations and model simulations for recent climate9, 10. We conclude that the mechanism behind solar forcing of regional climate change may have been similar under both modern and Last Glacial Maximum climate conditions.

Description: Although ocean warming and acidification are recognized as two major anthropogenic perturbations of today’s oceans we know very little about how marine phytoplankton may respond via evolutionary change. We tested for adaptation to ocean warming in combination with ocean acidification in the globally important phytoplankton species Emiliania huxleyi. Temperature adaptation occurred independently of ocean acidification levels. Growth rates were up to 16% higher in populations adapted for one year to warming when assayed at their upper thermal tolerance limit. Particulate inorganic (PIC) and organic (POC) carbon production was restored to values under present-day ocean conditions, owing to adaptive evolution, and were 101% and 55% higher under combined warming and acidification, respectively, than in non-adapted controls. Cells also evolved to a smaller size while they recovered their initial PIC:POC ratio even under elevated CO2. The observed changes in coccolithophore growth, calcite and biomass production, cell size and elemental composition demonstrate the importance of evolutionary processes for phytoplankton performance in a future ocean.

Description: The origin of novel phenotypic characters is a key component in organismal diversification; yet, the mechanisms underlying the emergence of such evolutionary novelties are largely unknown. Here we examine the origin of egg-spots, an evolutionary innovation of the most species-rich group of cichlids, the haplochromines, where these conspicuous male fin colour markings are involved in mating. Applying a combination of RNAseq, comparative genomics and functional experiments, we identify two novel pigmentation genes, fhl2a and fhl2b, and show that especially the more rapidly evolving b-paralog is associated with egg-spot formation. We further find that egg-spot bearing haplochromines, but not other cichlids, feature a transposable element in the cis-regulatory region of fhl2b. Using transgenic zebrafish, we finally demonstrate that this region shows specific enhancer activities in iridophores, a type of pigment cells found in egg-spots, suggesting that a cis-regulatory change is causally linked to the gain of expression in egg-spot bearing haplochromines

Description: Precipitation is highly variable in space and time; hence, rain gauge time series generally exhibit additional random small-scale variability compared to area averages. Therefore, differences between daily precipitation statistics simulated by climate models and gauge observations are generally not only caused by model biases, but also by the corresponding scale gap. Classical bias correction methods, in general, cannot bridge this gap; they do not account for small-scale random variability and may produce artifacts. Here, stochastic model output statistics is proposed as a bias correction framework to explicitly account for random small-scale variability. Daily precipitation simulated by a regional climate model (RCM) is employed to predict the probability distribution of local precipitation. The pairwise correspondence between predictor and predictand required for calibration is ensured by driving the RCM with perfect boundary conditions. Wet day probabilities are described by a logistic regression, and precipitation intensities are described by a mixture model consisting of a gamma distribution for moderate precipitation and a generalized Pareto distribution for extremes. The dependence of the model parameters on simulated precipitation is modeled by a vector generalized linear model. The proposed model effectively corrects systematic biases and correctly represents local-scale random variability for most gauges. Additionally, a simplified model is considered that disregards the separate tail model. This computationally efficient model proves to be a feasible alternative for precipitation up to moderately extreme intensities. The approach sets a new framework for bias correction that combines the advantages of weather generators and RCMs.

Description: Between 1965 and 1990, the waters of the Nordic Seas and the subpolar basins of the North Atlantic Ocean freshened substantially1. The Arctic Ocean also became less saline over this time, as a consequence of increasing runoff1, 2, 3, 4, but it is not clear whether flow from the Arctic Ocean was the main source of the Nordic Seas salinity anomaly. As a region of deep-water formation, the Nordic Seas are central to the Atlantic meridional overturning circulation, but this process is inhibited if the surface salinity is too low2. Here we use the instrumental record of Nordic Seas hydrography, along with a global ocean–sea-ice model hindcast simulation, to identify the sources and magnitude of freshwater that has accumulated in the Nordic Seas since 1950. We find that the freshwater anomalies within the Nordic Seas can mostly be explained by less salt entering the southern part of the basin with the relatively saline Atlantic inflow, with seemingly little contribution from the Arctic Ocean. We conclude that hydrographic changes in the Nordic Seas are primarily related to changes in the Atlantic Ocean. We infer that if the Atlantic inflow and Nordic Seas both freshen similarly, this would render the Atlantic meridional overturning circulation relatively insensitive to Nordic Seas freshwater content.

Description: There is an ongoing discussion in the community concerning the wave-averaged momentum equations in the hybrid vertically Lagrangian and horizontally Eulerian (VL) framework and, in particular, the form stress term (representing the residual effect of pressure perturbations) which is thought to restrict the handling of higher order waves in terms of a perturbation expansion. The present study shows that the traditional pressure-based form stress term can be transformed into a set of terms that do not contain any pressure quantities but do contain the time derivative of a wave-induced velocity. This wave-induced velocity is referred to as the pseudomomentum in the VL framework, as it is analogous to the generalized pseudomomentum in Andrews and McIntyre. This enables the second expression for the wave-averaged momentum equations in the VL framework (this time for the development of the total transport velocity minus the VL pseudomomentum) to be derived together with the vortex force. The velocity-based expression of the form stress term also contains the residual effect of the turbulent viscosity, which is useful for understanding the dissipation of wave energy leading to transfer of momentum from waves to circulation. It is found that the concept of the virtual wave stress of Longuet-Higgins is applicable to quite general situations: it does not matter whether there is wind forcing or not, the waves can have slow variations, and the viscosity coefficient can vary in the vertical. These results provide a basis for revisiting the surface boundary condition used in numerical circulation models.

Description: Mooring observations and model simulations point to an instability of the Labrador Current (LC) during winter, with enhanced eddy kinetic energy (EKE) at periods between 2 to 5 days, and much less EKE during other seasons. Linear stability analysis using vertical shear and stratification from the model reveals three dominant modes of instability in the LC: - a balanced interior mode with along-flow wavelengths of about 30–45 km, phase velocities of 0.3 m/s, maximal growth rates of 1 d−1 and surface intensified, but deep reaching amplitudes, - a balanced shallow mode with along-flow wavelengths of about 0.3–1.5 km, about three times larger phase speeds and growth rates, but amplitudes confined to the mixed layer (ML), - and an unbalanced symmetric mode with largest growth rates, vanishing phase speeds and along-flow structure, and very small cross-flow wavelengths, also confined to the ML. Both balanced modes are akin to baroclinic instability, but operate at moderate to small Richardson numbers Ri with much larger growth rates as for the quasi-geostrophic limit of Ri ≫ 1. The interior mode is found to be responsible for the instability of the LC during winter. Weak stratification and enhanced vertical shear due to local buoyancy loss and the advection of convective water masses from the interior result in small Ri within the LC, and to three times larger growth rates of the interior mode in March compared to summer and fall conditions. Both the shallow and the symmetric mode are not resolved by the model, but it is suggested that they might also play an important role for the instability in the LC and for lateral mixing.

Description: Sensible and latent heat fluxes were estimated from turbulence measurements gathered during several Atlantic transects of the R/V Polarstern. The inertial dissipation method was used to analyze the data. Resulting bulk transfer coefficients were then applied to the data from the ship’s meteorological system to get continuous time series of the heat fluxes. Combined to the measured downward solar and longwave radiation fluxes allows for an estimate of the total energy budget at the air-sea interface. Comparing these parameterized energy fluxes to ones based on the COARE 3.0 bulk flux algorithm show very strong agreement.

Description: Hydrothermal flow at oceanic spreading centres accounts for about ten per cent of all heat flux in the oceans and controls the thermal structure of young oceanic plates. It also influences ocean and crustal chemistry, provides a basis for chemosynthetic ecosystems, and has formed massive sulphide ore deposits throughout Earth’s history. Despite this, how and under what conditions heat is extracted, in particular from the lower crust, remains largely unclear. Here we present high-resolution, whole-crust, two- and three-dimensional simulations of hydrothermal flow beneath fast-spreading ridges that predict the existence of two interacting flow components, controlled by different physical mechanisms, that merge above the melt lens to feed ridge-centred vent sites. Shallow on-axis flow structures develop owing to the thermodynamic properties of water, whereas deeper off-axis flow is strongly shaped by crustal permeability, particularly the brittle–ductile transition. About 60 per cent of the discharging fluid mass is replenished on-axis by warm (up to 300 degrees Celsius) recharge flow surrounding the hot thermal plumes, and the remaining 40 per cent or so occurs as colder and broader recharge up to several kilometres away from the axis that feeds hot (500–700 degrees Celsius) deep-rooted off-axis flow towards the ridge. Despite its lower contribution to the total mass flux, this deep off-axis flow carries about 70 per cent of the thermal energy released at the ridge axis. This combination of two flow components explains the seismically determined thermal structure of the crust and reconciles previously incompatible models favouring either shallower on-axis or deeper off-axis hydrothermal circulation.

Description: Nitrogen fixation, the biological reduction of dinitrogen gas (N2) to ammonium (NH4+), is quantitatively the most important external source of new nitrogen (N) to the open ocean. Classically, the ecological niche of oceanic N2 fixers (diazotrophs) is ascribed to tropical oligotrophic surface waters, often depleted in fixed N, with a diazotrophic community dominated by cyanobacteria. Although this applies for large areas of the ocean, biogeochemical models and phylogenetic studies suggest that the oceanic diazotrophic niche may be much broader than previously considered, resulting in major implications for the global N-budget. Here, we report on the composition, distribution and abundance of nifH, the functional gene marker for N2 fixation. Our results show the presence of eight clades of diazotrophs in the oxygen minimum zone (OMZ) off Peru. Although proteobacterial clades dominated overall, two clusters affiliated to spirochaeta and archaea were identified. N2 fixation was detected within OMZ waters and was stimulated by the addition of organic carbon sources supporting the view that non-phototrophic diazotrophs were actively fixing dinitrogen. The observed co-occurrence of key functional genes for N2 fixation, nitrification, anammox and denitrification suggests that a close spatial coupling of N-input and N-loss processes exists in the OMZ off Peru. The wide distribution of diazotrophs throughout the water column adds to the emerging view that the habitat of marine diazotrophs can be extended to low oxygen/high nitrate areas. Furthermore, our statistical analysis suggests that NO2− and PO43− are the major factors affecting diazotrophic distribution throughout the OMZ. In view of the predicted increase in ocean deoxygenation resulting from global warming, our findings indicate that the importance of OMZs as niches for N2 fixation may increase in the futur

Description: The dynamical origin of the spectral and autocorrelation structure of annular variability in the troposphere is investigated by a deductive approach. Specifically, the structure of the power spectrum and autocorrelation function of the zonal-mean geopotential is analyzed for the case of a quasigeostrophic spherical atmosphere subject to a white noise mechanical forcing applied in a single Hough mode and concentrated at a particular level in the vertical, with vertically uniform Newtonian cooling and Rayleigh drag concentrated at a rigid lower boundary. Analytic expressions for the power spectrum are presented together with expressions for an approximate red noise (i.e., a Lorentzian-shaped) power spectrum. It is found that for an infinitely deep atmosphere the power spectrum can be well approximated by a red noise process for the first few Hough modes (associated with large Rossby heights), provided the distance from the forcing is not larger than about one Rossby height. When a frictional rigid lower boundary is included, however, the approximation is generally bad. The high-frequency part of the power spectrum exhibits near-exponential behavior and the autocorrelation function shows a transition from a rapid decay at short lags to a much slower decay at longer lags, if the thermal and mechanical damping time scales are sufficiently well separated. Since observed annular variability exhibits the same characteristics, the above results lead to the hypothesis that these characteristics may, to some extent, be intrinsic to the linear zonal-mean response problem—although the need for an additional contribution from eddy feedbacks is also implied by the results.

Description: A representation of an equatorial basin mode excited in a shallow water model for a single high order baroclinic vertical normal mode is used as a simple model for the equatorial deep jets. The model is linearized about both a state of rest and a barotropic mean flow corresponding to the observed Atlantic Equatorial Intermediate Current System. We found that the eastward mean flow associated with the North and South Intermediate Counter Currents (NICC and SICC, respectively) effectively shields the Equator from off-equatorial Rossby waves. The westward propagation of these waves is blocked and focusing on the Equator due to beta dispersion is prevented. This leads to less energetic jets along the Equator. On the other hand, the westward barotropic mean flow along the Equator reduces the gradient of absolute vorticity and hence widens the cross-equatorial structure of the basin mode. Increasing lateral viscosity predominantly affects the width of the basin modes’ Kelvin wave component in the presence of the mean flow while the Rossby wave is confined by the flanking NICC and SICC. Independent of the presence of the mean flow, the application of sufficient lateral mixing also hinders the focusing of off-equatorial Rossby waves, which is hence an unlikely feature of a low-frequency basin mode in the real ocean.

Description: A decadal change in the character of ENSO was observed around year 2000 toward weaker-amplitude, higher-frequency events with an increased occurrence of central Pacific El Niños. Here these changes are assessed in terms of the Bjerknes stability index (BJ index), which is a measure of the growth rate of ENSO-related SST anomalies. The individual terms of the index are calculated from ocean reanalysis products separately for the time periods 1980–99 and 2000–10. The spread between the products is large, but they show a robust weakening of the thermocline feedback due to a reduced thermocline slope response to anomalous zonal wind stress as well as a weakened wind stress response to eastern equatorial Pacific SST anomalies. These changes are consistent with changes in the background state of the tropical Pacific: cooler mean SST in the eastern and central equatorial Pacific results in reduced convection there together with a westward shift in the ascending branch of the Walker circulation. This shift leads to a weakening in the relationship between eastern Pacific SST and longitudinally averaged equatorial zonal wind stress. Also, despite a steeper mean thermocline slope in the more recent period, the thermocline slope response to wind stress anomalies weakened due to a smaller zonal wind fetch that results from ENSO-related wind anomalies being more confined to the western basin. As a result, the total BJ index is more negative, corresponding to a more strongly damped system in the past decade compared to the 1980s and 1990s.

Description: The realization that mitigation efforts to reduce CO2 emissions have, until now, been relatively ineffective has led to an increasing interest in climate engineering as a possible means of preventing potentially catastrophic consequences of climate change. While many studies have addressed the potential effectiveness of individual methods there have been few attempts to compare them. We use an Earth system model to compare the effectiveness and side effects of afforestation, artificial ocean upwelling, ocean iron fertilization, ocean alkalinization, and solar radiation management during a high CO2-emissions scenario. We find that even when applied continuously and at scales as large as currently deemed possible, all methods are, individually, either relatively ineffective with limited (〈8%) warming reductions, or they have severe side effects and cannot be stopped without causing rapid climate change. Our simulations suggest that the potential for these types of climate engineering to make up for failed mitigation may be very limited.

Description: In his comment, G. Bürger criticizes the conclusion that inflation of trends by quantile mapping is an adverse effect.He assumes that the argument would be ‘‘based on the belief that long-term trends and along with them future climate signals are to be large scale.’’ His line of argument reverts to the so-called inflated regression. Here it is shown, by referring to previous critiques of inflation and standard literature in statistical modeling as well as weather forecasting, that inflation is built upon a wrong understanding of explained versus unexplained variability and prediction versus simulation. It is argued that a sound regressionbased downscaling can in principle introduce systematic local variability in long-term trends, but inflation systematically deteriorates the representation of trends. Furthermore, it is demonstrated that inflation by construction deteriorates weather forecasts and is not able to correctly simulate small-scale spatiotemporal structure.

Description: Geophysical evidence suggests that fluids along fault planes have an important role in generating earthquakes; however, the nature of these fluids has not been well defined. The 2011 magnitude 9.0 Tohoku-Oki earthquake ruptured the interface between the subducting Pacific plate and the overlying Okhotsk plate. Here we report a sharp increase in mantle-derived helium in bottom seawater near the rupture zone 1 month after the earthquake. The timing and location indicate that fluids were released from the mantle on the seafloor along the plate interface. The movement of the fluids was rapid, with a velocity of ~4 km per day and an uncertainty factor of four. This rate is much faster than what would be expected from pressure-gradient propagation, suggesting that over-pressurized fluid is discharged along the plate interface.

Description: The relationship between the Agulhas Current and the Agulhas leakage is not well understood. Here, this is investigated using two basin-scale and two global ocean models, of incrementally increasing resolution. The response of the Agulhas Current is evaluated under a series of sensitivity experiments, in which idealised anomalies, designed to geometrically modulate zonal trade wind stress, are applied across the Indian Ocean basin. The imposed wind stress changes exceed ±2 standard deviations from the annual mean trade winds and, in the case of intensification, are partially representative of recently observed trends. The Agulhas leakage is quantified using complimentary techniques based on Lagrangian virtual floats and Eulerian passive tracer flux. As resolution increases, model behavior converges and the sensitivity of the leakage to Agulhas Current transport anomalies is reduced. In the two eddy-resolving configurations tested, the leakage is insensitive to changes in Agulhas Current transport at 32°S, though substantial eddy kinetic energy anomalies are evident. Consistent with observations, the position of the retroflection remains stable. The decoupling of Agulhas Current variability from the Agulhas leakage suggests that, while correlations between the two may exist, they may not have a clear dynamical basis. It is suggested that present and future Agulhas leakage proxies be considered in the context of potentially transient forcing regimes.

Description: In the oceans’ high-nitrate–low-chlorophyll regions, such as the Peru/Humboldt Current system and the adjacent eastern equatorial Pacific1, primary productivity is limited by the micronutrient iron. Within the Peruvian upwelling area, bioavailable iron is released from the reducing continental margin sediments2. The magnitude of this seafloor source could change with fluctuations in the extension or intensity of the oxygen minimum zones3, 4. Here we show that measurements of molybdenum, uranium and iron concentrations can be used as a proxy for sedimentary iron release, and use this proxy to assess iron release from the sea floor beneath the Peru upwelling system during the past 140,000 years. We observe a coupling between levels of denitrification, as indicated by nitrogen isotopes, trace metal proxies for oxygenation, and sedimentary iron concentrations. Specifically, periods with poor upper ocean oxygenation are characterized by more efficient iron retention in the sediment and a diminished iron supply to the water column. We attribute efficient iron retention under more reducing conditions to widespread sulphidic conditions in the surface sediment and concomitant precipitation of iron sulphides. We argue that iron release from continental margin sediments is most effective in a narrow redox window where neither oxygen nor sulphide is present. We therefore suggest that future deoxygenation in the Peru upwelling area would be unlikely to result in increased iron availability, whereas in weaker oxygen minimum zones partial deoxygenation may enhance the iron supply.

Description: Animal burrowing and sediment-mixing (bioturbation) began during the run up to the Ediacaran/Cambrian boundary1, 2, 3, initiating a transition4, 5 between the stratified Precambrian6 and more well-mixed Phanerozoic7 sedimentary records, against the backdrop of a variable8, 9 global oxygen reservoir probably smaller in size than present10, 11. Phosphorus is the long-term12 limiting nutrient for oxygen production via burial of organic carbon13, and its retention (relative to carbon) within organic matter in marine sediments is enhanced by bioturbation14, 15, 16, 17, 18. Here we explore the biogeochemical implications of a bioturbation-induced organic phosphorus sink in a simple model. We show that increased bioturbation robustly triggers a net decrease in the size of the global oxygen reservoir—the magnitude of which is contingent upon the prescribed difference in carbon to phosphorus ratios between bioturbated and laminated sediments. Bioturbation also reduces steady-state marine phosphate levels, but this effect is offset by the decline in iron-adsorbed phosphate burial that results from a decrease in oxygen concentrations. The introduction of oxygen-sensitive bioturbation to dynamical model runs is sufficient to trigger a negative feedback loop: the intensity of bioturbation is limited by the oxygen decrease it initially causes. The onset of this feedback is consistent with redox variations observed during the early Cambrian rise of bioturbation, leading us to suggest that bioturbation helped to regulate early oxygen and phosphorus cycles.

Description: Assessments of climate sensitivity to projected greenhouse gas concentrations underpin environmental policy decisions, with such assessments often based on model simulations of climate during recent centuries and millennia1, 2, 3. These simulations depend critically on accurate records of past aerosol forcing from global-scale volcanic eruptions, reconstructed from measurements of sulphate deposition in ice cores4, 5, 6. Non-uniform transport and deposition of volcanic fallout mean that multiple records from a wide array of ice cores must be combined to create accurate reconstructions. Here we re-evaluated the record of volcanic sulphate deposition using a much more extensive array of Antarctic ice cores. In our new reconstruction, many additional records have been added and dating of previously published records corrected through precise synchronization to the annually dated West Antarctic Ice Sheet Divide ice core7, improving and extending the record throughout the Common Era. Whereas agreement with existing reconstructions is excellent after 1500, we found a substantially different history of volcanic aerosol deposition before 1500; for example, global aerosol forcing values from some of the largest eruptions (for example, 1257 and 1458) previously were overestimated by 20–30% and others underestimated by 20–50%.

Description: A surface diurnal warm layer is diagnosed from Seaglider observations, and develops on half the days in the CINDY/DYNAMO Indian Ocean experiment. The diurnal warm layer occurs on days of high solar radiation flux (〉 80 W m−2) and low wind speed (〈 6 m s−1), and preferentially in the inactive stage of the Madden–Julian Oscillation. Its diurnal harmonic has an exponential vertical structure with a depth scale of 4–5 m (dependent on chlorophyll concentration), consistent with forcing by absorption of solar radiation. The effective sea surface temperature (SST) anomaly due to the diurnal warm layer often reaches 0.8°C in the afternoon, with a daily mean of 0.2°C, rectifying the diurnal cycle onto longer time scales. This SST anomaly drives an anomalous flux of 4 W m−2 that cools the ocean. Alternatively, in a climate model where this process is unresolved, this represents an erroneous flux that warms the ocean. A simple model predicts a diurnal warm layer to occur on 30–50% of days across the tropical warm pool. On the remaining days, with low solar radiation and high wind speeds, a residual diurnal cycle is observed by the Seaglider, with a diurnal harmonic of temperature that decreases linearly with depth. As wind speed increases, this already weak temperature gradient decreases further, tending towards isothermal conditions.

Description: The exchange of water masses across the Antarctic continental shelf break regulates the export of dense shelf waters to depth as well as the transport of warm, mid-depth waters towards ice shelves and glacial grounding lines1. The penetration of the warmer mid-depth waters past the shelf break has been implicated in the pronounced loss of ice shelf mass over much of west Antarctica2, 3, 4. In high-resolution, regional circulation models, the Antarctic shelf break hosts an energetic mesoscale eddy field5, 6, but observations that capture this mesoscale variability have been limited. Here we show, using hydrographic data collected from ocean gliders, that eddy-induced transport is a primary contributor to mass and property fluxes across the slope. Measurements along ten cross-shelf hydrographic sections show a complex velocity structure and a stratification consistent with an onshore eddy mass flux. We show that the eddy transport and the surface wind-driven transport make comparable contributions to the total overturning circulation. Eddy-induced transport is concentrated in the warm, intermediate layers away from frictional boundaries. We conclude that understanding mesoscale dynamics will be critical for constraining circumpolar heat fluxes and future rates of retreat of Antarctic ice shelves.

Description: Sea surface temperature (SST) anomalies in the eastern equatorial Atlantic are connected to modulations in the strength of the South Atlantic subtropical high-pressure system, referred to as the South Atlantic Anticyclone (SAA). Using ocean and atmosphere reanalysis products we show here that the strength of the SAA from February to May impacts the timing of the cold tongue onset and the intensity of its development in the eastern equatorial Atlantic (EEA) via anomalous tropical wind power. This modulation of the timing and amplitude of the seasonal cold tongue development manifests as anomalous SST events peaking between June and August. The timing and impact of this connection is not completely symmetric for warm and cold events. For cold events, an anomalously strong SAA in February and March leads to positive wind power anomalies from February to June resulting in an early cold tongue onset and subsequent cold SST anomalies in June and July. For warm events the anomalously weak SAA persists until May, generating negative wind power anomalies that lead to a late cold tongue onset as well as a suppression of the cold tongue development and associated warm SST anomalies. Mechanisms by which SAA induced wind power variations south of the equator influence EEA SST are discussed, including ocean adjustment via Rossby and Kelvin wave propagation, meridional advection, and local intraseasonal wind variations

Description: Stratospheric water vapour is a powerful greenhouse gas. The longest available record from balloon observations over Boulder, Colorado, USA shows increases in stratospheric water vapour concentrations that cannot be fully explained by observed changes in the main drivers, tropical tropopause temperatures and methane. Satellite observations could help resolve the issue, but constructing a reliable long-term data record from individual short satellite records is challenging. Here we present an approach to merge satellite data sets with the help of a chemistry-climate model nudged to observed meteorology. We use the models' water vapour as a transfer function between data sets that overcomes issues arising from instrument drift and short overlap periods. In the lower stratosphere, our water vapour record extends back to 1988 and water vapour concentrations largely follow tropical tropopause temperatures. Lower and mid-stratospheric long-term trends are negative, and the trends from Boulder are shown not to be globally representative. In the upper stratosphere, our record extends back to 1986 and shows positive long-term trends. The altitudinal differences in the trends are explained by methane oxidation together with a strengthened lower-stratospheric and a weakened upper-stratospheric circulation inferred by this analysis. Our results call into question previous estimates of surface radiative forcing based on presumed global long-term increases in water vapour concentrations in the lower stratosphere.

Description: Large earthquakes on mid-ocean ridge transform faults are commonly preceded by foreshocks1, 2, 3 and changes in the seismic properties of the fault zone3. These seismic precursors could be linked to fluid-related processes2, 3. Hydrothermal fluids within young, hot crust near the intersection of oceanic transform faults are probably in a supercritical condition4. At constant temperature, supercritical fluids become significantly more compressible with decreasing pressure, with potential impacts on fault behaviour. Here we use a theoretical model to show that oceanic transform faults can switch from dilatant and progressive deformation to rupture in response to fluid-related processes. We assume that the fault core material behaves according to a Cam-clay-type5 constitutive law, which is commonly used to account for the behaviour of clays. According to our model, we find that the fault is initially stable, with stresses gradually increasing over a timescale of years in response to tectonic loading. The fault evolves into a metastable phase, lasting a few days, during which the fault rocks dilate and pore pressures decrease, causing the compressibility of the supercritical fluids to increase. This in turn triggers fault-slip instability that creates foreshock swarms. In the final phase, the fault fails in the mainshock rupture. Our results imply that seismic precursors are caused by changes in fluid pressure which result in variations in fluid compressibility, in response to rock deformation just before rupture.

Description: We present a detailed quality assessment of a novel underwater sensor for the measurement of CO2 partial pressure (pCO2) based on surface water field deployments carried out between 2008 and 2011. The commercially available sensor, which is based on membrane equilibration and NDIR spectrometry is small and can be integrated into mobile platforms. It is calibrated in water against a proven flow-through pCO2 instrument within a custom-built calibration setup. The aspect of highest concern with respect to achievable data quality of the sensor is the compensation for signal drift inevitably connected to absorption measurements. We use three means to correct for drift effects: (i) a filter correlation or dual-beam setup, (ii) regular zero gas measurements realized automatically within the sensor and (iii) a zero-based transformation of two sensor calibrations flanking the time of sensor deployment. Three sensors were tested against an underway pCO2 system during two major research cruises providing an in situ temperature range from 7.4 to 30.1°C and pCO2 values between 289 and 445 μatm. The average difference between sensor and reference pCO2 was found to be -0.6 ± 3 μatm with a RMSE of 3.7 μatm.

Description: The Agulhas Current (AC) is the strongest western boundary current in the Southern Hemisphere and is key for weather and climate patterns, both regionally and globally. Its heat transfer into both the midlatitude South Indian Ocean and South Atlantic is of global significance. A new composite coral record (Ifaty and Tulear massive Porites corals), is linked to historical AC sea surface temperature (SST) instrumental data, showing robust correlations. The composite coral SST data start in 1660 and comprise 200 years more than the AC instrumental record. Numerical modelling exhibits that this new coral derived SST record is representative for the wider core region of the AC. AC SSTs variabilities show distinct cooling through the Little Ice Age and warming during the late 18th, 19th and 20th century, with significant decadal variability superimposed. Furthermore, the AC SSTs are teleconnected with the broad southern Indian and Atlantic Oceans, showing that the AC system is pivotal for inter-ocean heat exchange south of Africa.

Description: Large igneous province subduction is a rare process on Earth. A modern example is the subduction of the oceanic Hikurangi Plateau beneath the southern Kermadec arc, offshore New Zealand. This segment of the arc has the largest total lava volume erupted and the highest volcano density of the entire Kermadec arc. Here we show that Kermadec arc lavas south of B32°S have elevated Pb and Sr and low Nd isotope ratios, which argues, together with increasing seafloor depth, forearc retreat and crustal thinning, for initial Hikurangi Plateau—Kermadec arc collision B250 km north of its present position. The combined data set indicates that a much larger portion of the Hikurangi Plateau (the missing Ontong Java Nui piece) than previously believed has already been subducted. Oblique plate convergence caused southward migration of the thickened and buoyant oceanic plateau crust, creating a buoyant ‘Hikurangi’ me´lange beneath the Moho that interacts with ascending arc melts.

Description: Ammassalik in southeast Greenland is known for strong wind events that can reach hurricane intensity and cause severe destruction in the local town. Yet, these winds and their impact on the nearby fjord and shelf region have not been studied in detail. Here, data from two meteorological stations and the European Centre for Medium-Range Weather Forecasts Interim Re-Analysis (ERA-Interim) are used to identify and characterize these strong downslope wind events, which are especially pronounced at a major east Greenland fjord, Sermilik Fjord, within Ammassalik. Their local and regional characteristics, their dynamics and their impacts on the regional sea ice cover, and air–sea fluxes are described. Based on a composite of the events it is concluded that wind events last for approximately a day, and seven to eight events occur each winter. Downslope wind events are associated with a deep synoptic-scale cyclone between Iceland and Greenland. During the events, cold dry air is advected down the ice sheet. The downslope flow is accelerated by gravitational acceleration, flow convergence inside the Ammassalik valley, and near the coast by an additional thermal and synoptic-scale pressure gradient acceleration. Wind events are associated with a large buoyancy loss over the Irminger Sea, and it is estimated that they drive one-fifth of the net wintertime loss. Also, the extreme winds drive sea ice out of the fjord and away from the shelf.

Description: In 2013, the vast majority of the monitored climate variables reported here maintained trends established in recent decades. ENSO was in a neutral state during the entire year, remaining mostly on the cool side of neutral with modest impacts on regional weather patterns' around the world. This follows several years dominated by the effects of either La Nina. or El Nino events. According to several independent analyses, 2013 was again among the 10 warmest years on record at the global scale, both at the Earth's surface and through the troposphere. Some regions in the Southern Hemispherehad record or near-record high temperatures for the year. Australia observed its hottest year on record, while Argentina and New Zealand reported their second and third hottest years, respectively. In Antarctica, Amundsen-Scott South Pole Station reported its highest annual temperature since records began in 1957 At the opposite pole, the Arctic observed its seventh warmest year since record's began in the early 20th century. At 20-m depth, record high temperatures were measured at some permafrost stations on the North Slope Of Alaska and in the Brooks Range. In the Northern Hemisphere extratropics, anomalous meridional atmospheric circulation occurred throughout much of the year leading to marked regional extremes of both temperature and precipitation. Cold temperature anomalies during Winter across Eurasia were followed by warm Spring temperature anomalies, which, were linked to a new record Eurasian snow cover extent in the May. Minimum sea ice extent in the :Arctic was the sixth lowest since satellite Observations began in 1979. Including 2013, all seven lowest extents on record have occurred in the past seven years Antarctica, on the other hand, had above average sea ice extent throughout 2013, with 116 days Of new daily high extent records, inclding a new daily maximum sea ice area of 19.57 million km(2) reached on 1 October. ENSO-neutral conditions in the eastern central Pacific Ocean and a negative Pacific decadal oscillation pattern in the North Pacific had the largest impacts on the global sea surface temperature in 2013: The North Pacific reached a historic high temperature in 2013 and on balance the globally-averaged sea surface temperature was among the 10 highest on record. Overall, the salt Content in near-surface ocean waters increased while in intermediate waters it decreased. Global mean sea level continued to rise during 2013, on pace with a trend of 3,2 mm yr(-1) over the past two decades. A portion of this trend (0.5 mm yr(-1)) has been attributed to natural variability associated with the Pacific decadal oscillation as Well as to ongoing contribution from the melting of glaciers and ice sheets and ocean warming. Global tropical cyclone frequency during 2013 was slightly above average with a total of 94 storms, although the North Atlantic Basin had its quietest hurricane season since 1994. In the Western North Pacific Basin, Super Typhoon Haiyan, the deadliest tropical Cyclone of 2013, had 1-minute sustained winds estimated to be 170 kt (OS m s(-1)) on 7 November, the highest Wind speed ever assigned to a tropical cyclone. High storm surge was also associated with Haiyan at it Made landfall over the central Philippines, an area where sea level is currently at historic highs increasing by 200 mm since 1970. In the atmosphere, carbon dioxide, methane, and nitrous oxide all Continued to increase in 2013. As in previous our years, each of these Major greenhouse gases once again reached historic high Concentrations. In the Arctic carbon dioxide and methane:, Increased at the same rate as:the global increase. These increases are likely due to export from lower latitudes rather than a consequence Of increases in Arctic sources such as thawing permafrost., At Mauna Loa, Hawaii, for the first time since measurement began in 1958, the daily average Mixing ratio Of carbon dioxide exceeded 400 ppm on 9 May. The state of these variables, along with dozens of others, and the 2013 climate conditions of regions around the world are discussed in further detail in this 24th, edition of the State of the Climate series

Description: Vitamin B 1 (thiamine pyrophosphate, TPP) is essential to all life but scarce in ocean surface waters. In many bacteria and a few eukaryotic groups thiamine biosynthesis genes are controlled by metabolite-sensing mRNA-based gene regulators known as riboswitches. Using available genome sequences and transcriptomes generated from ecologically important marine phytoplankton, we identified 31 new eukaryotic riboswitches. These were found in alveolate, cryptophyte, haptophyte and rhizarian phytoplankton as well as taxa from two lineages previously known to have riboswitches (green algae and stramenopiles). The predicted secondary structures bear hallmarks of TPP-sensing riboswitches. Surprisingly, most of the identified riboswitches are affiliated with genes of unknown function, rather than characterized thiamine biosynthesis genes. Using qPCR and growth experiments involving two prasinophyte algae, we show that expression of these genes increases significantly under vitamin B 1 -deplete conditions relative to controls. Pathway analyses show that several algae harboring the uncharacterized genes lack one or more enzymes in the known TPP biosynthesis pathway. We demonstrate that one such alga, the major primary producer Emiliania huxleyi, grows on 4-amino-5-hydroxymethyl-2-methylpyrimidine (a thiamine precursor moiety) alone, although long thought dependent on exogenous sources of thiamine. Thus, overall, we have identified riboswitches in major eukaryotic lineages not known to undergo this form of gene regulation. In these phytoplankton groups, riboswitches are often affiliated with widespread thiamine-responsive genes with as yet uncertain roles in TPP pathways. Further, taxa with 'incomplete' TPP biosynthesis pathways do not necessarily require exogenous vitamin B 1, making vitamin control of phytoplankton blooms more complex than the current paradigm suggests. © 2014 International Society for Microbial Ecology. All rights reserved.

Description: Rhodoliths are coralline red algal assemblages that commonly occur in marine habitats from the tropics to polar latitudes. They form rigid structures of high-magnesium calcite and have a good fossil record. Here I show that rhodoliths are ecosystem engineers in a high Arctic environment that increase local biodiversity by providing habitat. Gouged by boring mussels, originally solid rhodoliths become hollow ecospheres intensely colonised by benthic organisms. In the examined shelf areas, biodiversity in rhodolith-bearing habitats is significantly greater than in habitats without rhodoliths and hollow rhodoliths yield a greater biodiversity than solid ones. This biodiversity, however, is threatened because hollow rhodoliths take a long time to form and are susceptible to global change and anthropogenic impacts such as trawl net fisheries that can destroy hollow rhodoliths. Rhodoliths and other forms of coralline red algae play a key role in a plurality of environments and need improved management and protection plans.

Description: Submarine mud volcanoes are important sources of methane to the water column. However, the temporal variability of their mud and methane emissions is unknown. Methane emissions were previously proposed to result from a dynamic equilibrium between upward migration and consumption at the seabed by methane-consuming microbes. Here we show non-steady-state situations of vigorous mud movement that are revealed through variations in fluid flow, seabed temperature and seafloor bathymetry. Time series data for pressure, temperature, pH and seafloor photography were collected over 431 days using a benthic observatory at the active Hakon Mosby Mud Volcano. We documented 25 pulses of hot subsurface fluids, accompanied by eruptions that changed the landscape of the mud volcano. Four major events triggered rapid sediment uplift of more than a metre in height, substantial lateral flow of muds at average velocities of 0.4m per day, and significant emissions of methane and CO2 from the seafloor.

Description: Knowledge of concentrations and elemental ratios of suspended particles are important for understanding many biogeochemical processes in the ocean. These include patterns of phytoplankton nutrient limitation as well as linkages between the cycles of carbon and nitrogen or phosphorus. To further enable studies of ocean biogeochemistry, we here present a global dataset consisting of 100,605 total measurements of particulate organic carbon, nitrogen, or phosphorus analyzed as part of 70 cruises or time-series. The data are globally distributed and represent all major ocean regions as well as different depths in the water column. The global median C:P, N:P, and C:N ratios are 163, 22, and 6.6, respectively, but the data also includes extensive variation between samples from different regions. Thus, this compilation will hopefully assist in a wide range of future studies of ocean elemental ratios.

Description: The ability of coral reefs to engineer complex three-dimensional habitats is central to their success and the rich biodiversity they support. In tropical reefs, encrusting coralline algae bind together substrates and dead coral framework to make continuous reef structures, but beyond the photic zone, the cold-water coral Lophelia pertusa also forms large biogenic reefs, facilitated by skeletal fusion. Skeletal fusion in tropical corals can occur in closely related or juvenile individuals as a result of non-aggressive skeletal overgrowth or allogeneic tissue fusion, but contact reactions in many species result in mortality if there is no ‘self-recognition’ on a broad species level. This study reveals areas of ‘flawless’ skeletal fusion in Lophelia pertusa, potentially facilitated by allogeneic tissue fusion, are identified as having small aragonitic crystals or low levels of crystal organisation, and strong molecular bonding. Regardless of the mechanism, the recognition of ‘self’ between adjacent L. pertusa colonies leads to no observable mortality, facilitates ecosystem engineering and reduces aggression-related energetic expenditure in an environment where energy conservation is crucial. The potential for self-recognition at a species level, and subsequent skeletal fusion in framework-forming cold-water corals is an important first step in understanding their significance as ecological engineers in deep-seas worldwide.

Description: Cultivated bacteria such as actinomycetes are a highly useful source of biomedically important natural products. However, such ‘talented’ producers represent only a minute fraction of the entire, mostly uncultivated, prokaryotic diversity. The uncultured majority is generally perceived as a large, untapped resource of new drug candidates, but so far it is unknown whether taxa containing talented bacteria indeed exist. Here we report the single-cell- and metagenomics-based discovery of such producers. Two phylotypes of the candidate genus ‘Entotheonella’ with genomes of greater than 9 megabases and multiple, distinct biosynthetic gene clusters co-inhabit the chemically and microbially rich marine sponge Theonella swinhoei. Almost all bioactive polyketides and peptides known from this animal were attributed to a single phylotype. ‘Entotheonella’ spp. are widely distributed in sponges and belong to an environmental taxon proposed here as candidate phylum ‘Tectomicrobia’. The pronounced bioactivities and chemical uniqueness of ‘Entotheonella’ compounds provide significant opportunities for ecological studies and drug discovery.

Description: 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.

Description: The exponentially increasing number of sequenced genomes necessitates fast, accurate, universally applicable and automated approaches for the delineation of prokaryotic species. We developed specI (species identification tool; http://www.bork.embl.de/software/specI/), a method to group organisms into species clusters based on 40 universal, single-copy phylogenetic marker genes. Applied to 3,496 prokaryotic genomes, specI identified 1,753 species clusters. Of 314 discrepancies with a widely used taxonomic classification, 〉62% were resolved by literature support.

Description: The mammalian gastrointestinal tract, the site of digestion and nutrient absorption, harbors trillions of beneficial commensal microbes from all three domains of life. Commensal bacteria, in particular, are key participants in the digestion of food, and are responsible for the extraction and synthesis of nutrients and other metabolites that are essential for the maintenance of mammalian health. Many of these nutrients and metabolites derived from commensal bacteria have been implicated in the development, homeostasis and function of the immune system, suggesting that commensal bacteria may influence host immunity via nutrient- and metabolite-dependent mechanisms. Here we review the current knowledge of how commensal bacteria regulate the production and bioavailability of immunomodulatory, diet-dependent nutrients and metabolites and discuss how these commensal bacteria–derived products may regulate the development and function of the mammalian immune system.

Description: In bacteria, foreign nucleic acids are silenced by clustered, regularly interspaced, short palindromic repeats (CRISPR)--CRISPR-associated (Cas) systems. Bacterial type II CRISPR systems have been adapted to create guide RNAs that direct site-specific DNA cleavage by the Cas9 endonuclease in cultured cells. Here we show that the CRISPR-Cas system functions in vivo to induce targeted genetic modifications in zebrafish embryos with efficiencies similar to those obtained using zinc finger nucleases and transcription activator-like effector nucleases.

Description: Population genomics — in which genetic variation across the genome is studied in many individuals — has so far been limited to species for which reference genomes are available. A recent study shows how transcriptomics can be used to extend population genomics research across a far greater range of organisms. This advance promises important new insights int…

Description: The Denmark Strait Overflow (DSO) supplies about one-third of the North Atlantic Deep Water and is critical to global thermohaline circulation. Knowledge of the pathways of DSO through the Irminger Basin and its transformation there is still incomplete, however. The authors deploy over 10 000 Lagrangian particles at the Denmark Strait in a high-resolution ocean model to study these issues. First, the particle trajectories show that the mean position and potential density of dense waters cascading over the Denmark Strait sill evolve consistently with hydrographic observations. These sill particles transit the Irminger Basin to the Spill Jet section (65.25°N) in 5–7 days and to the Angmagssalik section (63.5°N) in 2–3 weeks. Second, the dense water pathways on the continental shelf are consistent with observations and particles released on the shelf in the strait constitute a significant fraction of the dense water particles recorded at the Angmagssalik section within 60 days (~25%). Some particles circulate on the shelf for several weeks before they spill off the shelf break and join the overflow from the sill. Third, there are two places where the water density following particle trajectories decreases rapidly due to intense mixing: to the southwest of the sill and southwest of the Kangerdlugssuaq Trough on the continental slope. After transformation in these places, the overflow particles exhibit a wide range of densities.

Description: Many marine sponges are hosts to dense and phylogenetically diverse microbial communities that are located in the extracellular matrix of the animal. The candidate phylum Poribacteria is a predominant member of the sponge microbiome and its representatives are nearly exclusively found in sponges. Here we used single-cell genomics to obtain comprehensive insights into the metabolic potential of individual poribacterial cells representing three distinct phylogenetic groups within Poribacteria. Genome sizes were up to 5.4 Mbp and genome coverage was as high as 98.5%. Common features of the poribacterial genomes indicated that heterotrophy is likely to be of importance for this bacterial candidate phylum. Carbohydrate-active enzyme database screening and further detailed analysis of carbohydrate metabolism suggested the ability to degrade diverse carbohydrate sources likely originating from seawater and from the host itself. The presence of uronic acid degradation pathways as well as several specific sulfatases provides strong support that Poribacteria degrade glycosaminoglycan chains of proteoglycans, which are important components of the sponge host matrix. Dominant glycoside hydrolase families further suggest degradation of other glycoproteins in the host matrix. We therefore propose that Poribacteria are well adapted to an existence in the sponge extracellular matrix. Poribacteria may be viewed as efficient scavengers and recyclers of a particular suite of carbon compounds that are unique to sponges as microbial ecosystems.

Description: Amplified marker-gene sequences can be used to understand microbial community structure, but they suffer from a high level of sequencing and amplification artifacts. The UPARSE pipeline reports operational taxonomic unit (OTU) sequences with ≤1% incorrect bases in artificial microbial community tests, compared with 〉3% incorrect bases commonly reported by other methods. The improved accuracy results in far fewer OTUs, consistently closer to the expected number of species in a community.

Description: Quantile mapping is routinely applied to correct biases of regional climate model simulations compared to observational data. If the observations are of similar resolution as the regional climate model, quantile mapping is a feasible approach. However, if the observations are of much higher resolution, quantile mapping also attempts to bridge this scale mismatch. Here, it is shown for daily precipitation that such quantile mapping-based downscaling is not feasible but introduces similar problems as inflation of perfect prognosis ("prog") downscaling: the spatial and temporal structure of the corrected time series is misrepresented, the drizzle effect for area means is overcorrected, area-mean extremes are overestimated, and trends are affected. To overcome these problems, stochastic bias correction is required.

Description: The climatic changes of the glacial cycles are thought to have been a major driver of population declines and species extinctions. However, studies to date have focused on terrestrial fauna and there is little understanding of how marine species responded to past climate change. Here we show that a true Arctic species, the bowhead whale (Balaena mysticetus), shifted its range and tracked its core suitable habitat northwards during the rapid climate change of the Pleistocene–Holocene transition. Late Pleistocene lineages survived into the Holocene and effective female population size increased rapidly, concurrent with a threefold increase in core suitable habitat. This study highlights that responses to climate change are likely to be species specific and difficult to predict. We estimate that the core suitable habitat of bowhead whales will be almost halved by the end of this century, potentially influencing future population dynamics.

Description: Ocean acidification, caused by the uptake of anthropogenic carbon dioxide, is a significant stressor to marine life. Ulf Riebesell charts the rapid rise in ocean acidification research, from the discovery of its adverse effects to its entry into the political consciousness.