M dwarfs are the most promising candidates for finding habitable worlds through atmospheric characterization. Planets in the habitable zone of low-mass stars experience intense tidal forcings and often become tidally locked. Despite the majority of research being centered on the climate dynamics of synchronously rotating planets in this scenario, synchronous rotation is not an inevitable outcome of tidal locking. Several different circumstances can result in an asynchronous rotation and, in some instances, can lead to spin-orbit resonances (SORs). We explore the climates of two different SOR scenarios with a coupled atmosphere-ocean general circulation climate model. Given the crucial role played by the oceans in shaping planetary climate, we adopt two different ocean tidal forcing parameterizations for each SOR scenario. Each of these cases is simulated with both a dynamic ocean and a thermodynamic ocean. Our findings reveal striking differences between the analyzed resonant case and the commonly studied synchronous rotation case. Periodic climate patterns are observed, with climatic features such as clouds and rainfall exhibiting a 60 degrees longitudinal shift relative to the substellar point. The evolution of quantities such as thermal emission and reflected light during a stellar period is noteworthy from the observational point of view, showing appreciable differences compared to the synchronous rotation scenario.

Abstract Wintertime open‐ocean convection is a key process in renewing deep water; however, the processes that promote convection on local scale remain poorly understood. We investigate the role of long‐lived anticyclonic eddies in facilitating deep convection in the Greenland Sea using a new model simulation and observations. We find a previously undocumented anticyclonic eddy in the Boreas Basin, in addition to a well‐observed anticyclonic eddy in the Greenland Basin. Both eddies feature year‐round lenses of weak stratification with upper‐domed isopycnals, facilitating convection over multiple winters.

The poleward warm Atlantic Water and returning cold water in the Nordic Seas play a crucial role in regulating the Northern Hemisphere climate. While previous studies have recognized the importance of mesoscale dynamics, a quantitative assessment of the role of mesoscale eddies in poleward heat transport is lacking. Our study investigates the role of eddies in poleward oceanic heat transport in the Nordic Seas using an ocean model where eddies are well represented. Using a novel configuration of the MITgcm ocean-ice model, we analyze 21 years of simulation. We show that eddy heat flux divergence offsets more than 70% of heat flux convergence induced by the mean flow along the Norwegian Atlantic Slope Current. Eddy heat flux divergence peaks at a depth of about 400 m near the thermocline and reaches a maximum near the steep Lofoten Escarpment. A temporal decomposition reveals that eddy heat flux divergence is stable on interannual timescales, although there is strong seasonality. Our study emphasizes the significant role of eddies in reducing poleward heat transport by diverting heat out of the Norwegian Atlantic Current into the Nordic Seas.

Abstract. We present the first multi-model study of the Antarctic sea ice response to enhanced meltwater due to dynamic mass loss from the Antarctic ice sheet. This meltwater flux (and its future increase under global warming) is not included in the most recent state-of-the-art climate model simulations used in CMIP6, representing a missing source of freshwater to the Southern Ocean. Previous climate model simulations have shown a wide range of responses in Antarctic sea ice and climate when this missing meltwater is introduced. Here, we analyze a new suite of 11 models comprising 43 ensemble members to assess the response to 0.1 Sv of Antarctic meltwater input at the ocean surface, evenly distributed around the Antarctic coastline under pre-industrial control forcing. Antarctic sea ice area increases in all models. However, there is a wide range in the response, with annual mean increases ranging from 0.71 to 4.14 million km2. There is also substantial variation in both the spatial distribution and the time scale of the sea ice response. The intermodel spread in sea ice response is influenced by the model mean-state sea ice area and volume, the prevalence of open-ocean deep convection, and the mean-state stratification of the ocean. These findings highlight the importance of model mean-state biases in determining the response to a missing Antarctic meltwater boundary condition.

Abstract. Atmospheric iodine has significant impacts on air quality, climate and human health. Its primary atmospheric source is a reaction on the sea surface between ozone and aqueous iodide (I-), which is naturally present in the ocean alongside iodate (IO3-) and organic iodine species. Here we describe a new global biogeochemical model of the marine iodine cycle, I-CYCLE, which predicts the distribution and cycling of iodide, iodate, phytoplankton associated iodine, detrital iodine and benthic iodine. I-CYCLE is embedded within the UKESM 1.0 ocean framework and driven by the MEDUSA biogeochemical model. In the model, the reduction of iodate to iodide is driven by uptake to plankton and subsequent release from particulate iodine reservoirs. Iodide is returned to iodate via two processes: biological oxidation coupled to ammonia oxidation, and a slow background reaction which may be abiotic. Below a specified oxygen threshold, iodate is reduced to iodide and the release of benthic and detrital iodine as iodide is amplified. Model parameters were tuned against observed iodide and iodate fields; the best-fit parameters are in good agreement with empirical estimates. The model replicates observed present day latitudinal and vertical trends in dissolved iodine speciation, as well as the impacts of oxygen minimum zones. Future iodine fields predicted for 2100 under the SSP585 scenario are presented.

The mixed layer of polynyas is vital for local climate as it determines the exchange of properties and energy between ocean, sea ice, and atmosphere. However, its evolution is poorly understood, as it is controlled by complex interactions among these components, yet highly undersampled, especially outside summer. Here, we present a 2-month, high vertical-resolution, full-depth hydrographic dataset from the southeastern Amundsen Sea polynya in austral autumn (from mid-February to mid-April 2014) collected by a recovered seal tag. This novel dataset quantifies the changes in upper- ocean temperature and salinity stratification in this previously unobserved season. Our seal-tag measurements reveal that the mixed layer experiences deepening, salinification, and intense heat loss through surface fl uxes. Heat and salt budgets suggest a sea ice formation rate of ; 3 cm per day. We use a one-dimensional model to reproduce the mixed layer evolution and further identify key controls on its characteristics. Our experiments with a range of reduced or amplified air-sea fl uxes show that heat loss to the atmosphere and related sea ice formation are the principal determinants of stratification evolution. Additionally, our modeling demonstrates that horizontal advection is required to fully explain the mixed layer evolution, underlining the importance of the ice-covered neighboring region for determining sea ice formation rates in the Amundsen Sea polynya. Our fi ndings suggest that the potential overestimation of sea ice production by satellite-based methods, due to the absence of oceanic heat fl ux, could be offset by horizontal advection inhibiting mixed layer deepening and sustaining sea ice formation.

The extratropical response to the Madden-Julian Oscillation (MJO) is modulated by two prominent modes of low-frequency sea surface temperature (SST) variability: the Atlantic Multidecadal Variability (AMV) and the Pacific Decadal Oscillation (PDO). Utilizing the UK Earth System Model (UKESM) 1100 year pre-industrial control simulation from CMIP6, this study offers a unique opportunity to explore decadal variability with an extensive dataset, surpassing the limitations of previous studies which focussed on reanalysis products. The results underscore a statistically significant influence of both AMV and PDO on the extratropical response across all MJO phases. Non-linear interactions between the MJO teleconnection and SST forcing are observed prominently in the modification of the response to MJO phase 6 (enhanced convection over the western Pacific), with AMV+ and PDO+ background states amplifying distinct teleconnection patterns, notably the negative North Atlantic Oscillation (NAO-) and the deepened Aleutian Low responses, respectively. These changes are greater in magnitude than would be expected from the linear superposition of the individual atmospheric responses to the SST mode and the MJO. The amplification of the MJO phase 6 teleconnection to the North Atlantic aligns with prior research based on ERA5 reanalysis data. While modulation of the response to MJO phase 3 (enhanced convection over the eastern Indian Ocean) is evident, it is less pronounced compared to phase 6, and the mechanisms via which it acts are less clear. Intriguingly, alterations in the teleconnection, such as a weaker Aleutian Low during PDO+, contradict the anticipated modulation. Since MJO phase 3 and PDO+ tend to weaken and strengthen the Aleutian Low, respectively, it would be reasonable to expect that these effects would cancel. Instead, the weakening of the Low after MJO phase 3 is increased during PDO+. A possible mechanism for the modulation of the teleconnections is a linear superposition of Rossby wave modes excited by the MJO, contingent upon the SST state. In the case of MJO phase 6, this corresponds to an amplification of the existing modes, and hence of the expected response. For MJO phase 3, however, there is an indication that other Rossby wave modes may also be excited in certain SST states, leading to interference which is out of phase with the primary response. Acknowledging the limitations of observational and reanalysis datasets, this study underscores the pivotal role of climate models in the effective study of decadal and multi-decadal variability. Importantly, the study has significant implications for extratropical forecasting over the coming decades. The modulation of the MJO teleconnection by AMV and PDO suggests modifications in predictability, crucial for refining forecasting techniques. Furthermore, these results provide a contextual foundation for studies examining MJO teleconnections in future climates, enabling a more accurate dissection of responses influenced by internal and anthropogenically forced variability.

Due to their abundance and their observational advantages, M dwarfs offer the best chance of finding habitable planets through sheer numbers. Therefore, in the race to detect signs of life beyond the Solar System, rocky M-dwarf planets offer exciting prospects. While the habitable zone serves as a preliminary indicator of the potential habitability of a planet, planetary climate studies are necessary in order to better assess a planet’s ability to host life. Climate is affected by numerous factors that are not considered in the classic habitable zone formulation, but can be included in climate models of varying complexity.Oceans have a dominant impact on planetary climate, so understanding their effects is a necessary part of modelling terrestrial exoplanets in order to understand future observations. We have conducted studies with an intermediate complexity coupled atmosphere-ocean general circulation model (FORTE2.0). Using a coupled dynamic ocean enables us to include effects of ocean circulation. Strong tidal interactions are tightly linked to the ocean vertical diffusivity and thus ocean temperature structure (including surface temperature). Taking into account the impact of ocean tides can therefore lead to significant effects on planetary climate.We investigated the case of non synchronous terrestrial planets in close orbits in the habitable zone of their M host star. In this scenario, we have parameterised the effect of propagating tides, and analysed their impact on ocean circulation and minimum and maximum values of surface temperature. We found that ocean tides are particularly important in setting latitudinal gradients in temperature, with subsequent effects on climate and habitability.By considering scenarios in which the magnitude of tidal forcings varies over a range of values, we were able to determine that key surface quantities (such as winds, heat flux and water flux) are subjected to change.The repercussions that ocean vertical diffusion can have on surface quantities is noteworthy from the observational point of view, as observable features - such as cloud patterns – are shaped differently in each scenario.

The Madden-Julian oscillation (MJO) is a key source of predictability for global weather. Through both tropospheric and stratospheric teleconnection pathways, the MJO is able to alter the extratropical circulation and, in turn, causes shifts in other modes of variability, such as the Pacific-North American pattern and North Atlantic oscillation. MJO teleconnections are known to vary on a range of time-scales, but their variability on decadal and multidecadal time-scales is not well understood. Using the UK Earth System Model 1 coupled climate model, we show that both Atlantic multidecadal variability (AMV) and the Pacific decadal oscillation (PDO) alter MJO teleconnection patterns and their impact on extratropical modes of variability. AMV and the PDO modulate the mean state of the atmosphere, in particular the Aleutian low, which controls how the circulation responds to the MJO. When the Aleutian low is deepened (e.g., during the positive phase of the PDO), this provides the conditions necessary for the MJO teleconnection to project onto the climatological low, either constructively or destructively. During the positive phase of the AMV and negative phase of the PDO, which favour a weak Aleutian low, the MJO cannot drive a significant cyclonic response in the region. Changes in the stratospheric polar vortex, preceded by MJO-related anomalies in the Aleutian low, also control extratropical weather. We hypothesise that this stratospheric teleconnection pathway is also modulated by both AMV and the PDO. These results have implications for improving the predictability of extratropical weather patterns over the coming decades. By understanding how MJO teleconnections are altered by internal modes of decadal and multidecadal variability, the impact of anthropogenic climate change can be better identified in future projections. This context will improve both long-range forecasts of MJO-driven variability and short-term forecasts in different sea-surface temperature conditions.

Tides play an important role in the circulation and mean state of the Earth’s oceans through inducing significant mixing. On other planets, tidal forcings could be highly amplified compared to Earth, such as planets orbiting relatively close to low-mass host stars, or planets having massive and/or close moons. The former scenario is especially important as, due to their abundance and their observational advantages, low-mass stars offer the best chance of finding habitable planets through sheer numbers. By varying the magnitude of tidal forcing over several orders of magnitude in a coupled atmosphere–ocean global circulation climate model, we find that key climatic quantities, such as heat transport intensity and both surface and deep ocean temperature, change with tidal strength in a nonlinear and nonmonotonic manner. We find an optimum value of tidal mixing, approximately 100 times that of Earth’s oceans, which minimizes climatic thermal gradients across the planet. In particular, we show that such planets are habitable for stellar flux values at which oceans with weaker or stronger tidal mixing freeze globally, suggesting an important role for ocean tidal mixing in planetary habitability.

Abstract We investigate the impacts of meltwater from Antarctic Ice Sheet (AIS) mass loss on New Zealand climate in a state‐of‐the‐art global climate model. We conduct simulations with additional meltwater from AIS mass loss for both the historical period and a high‐emissions future scenario. The ocean surface to the southeast of New Zealand cools, with the largest change in winter and spring. The additional meltwater results in a northward shift of the oceanic sub‐tropical front near New Zealand, which partially offsets the projected southward shift of this front in a warming climate. Wintertime surface westerly winds to the south of New Zealand also increase with the addition of the meltwater. The magnitude of the impact of Antarctic meltwater is uncertain due to the wide spread in estimates of Antarctic mass imbalance, but has important implications for future projections for New Zealand climate.

The Northeast Water Polynya is a significant annually recurring summertime Arctic polynya, located off the coast of Northeast Greenland. It is important for marine wildlife and affects local atmospheric and oceanic processes. In this study, over 40 years of observational and reanalysis products (ERA5 and ORAS5) are analysed to characterise the polynya's climatology and ascertain forcing mechanisms. The Northeast Water Polynya has high spatiotemporal variability; its location, size and structure vary interannually, and the period for which it is open is changing. We show this variability is largely driven by atmospheric forcing. The polynya extent is determined by the direction of the near-surface flow regime, and the relative locations of high and low sea-level pressure centers over the region. The surface conditions also impact the oceanic water column, which has a strong seasonal cycle in potential temperature and salinity, the amplitude of which decreases with depth. The ocean reanalyses also show a significant warming trend at all depths and a freshening near the surface consistent with greater ice melt, but salinification at lower depths (~ 200 m). As the Arctic region changes due to anthropogenic forcing, the sea-ice edge is migrating northwards and the Northeast Water Polynya is generally opening earlier and closing later in the year. This could have significant implications for both the atmosphere and ocean in this complex and rapidly changing environment.

This dataset is collected by a tag that was depolyed by a seal-tagging team onboard the RRS James Clark Ross, under the Ocean2ice project of the UK's Ice Sheet Stability Programme (Heywood et al. 2014). This tag (tag serial number: EM959; hereafter, EM959 for this tag) was attached to a male Southern Elephant Seal. EM959 was initially deployed on the Edwards Islands in Pine Island Bay, after which the instrumented seal moved west along the edge of the fast ice and grounded icebergs. This seal stayed in the southeastern corner of the Amundsen Sea Polynya from mid-February to mid-April (yearday 51.8-105.7). Thus, EM959 measured the upper-ocean properties of the Amundsen Sea Polynya continually for more than two months during austral autumn. In February 2020, another seal-tagging team onboard the RV Nathaniel B. Palmer, part of the International Thwaites Glacier Collaboration (ITGC) expedition to the Amundsen Sea, serendipitously found and recovered EM959. We calibrated EM959 conductivity data against nearby ship-based CTD profiles (i.e. the seven CTD casts within 10 km and 5 days of EM959 observations) obtained on the iSTAR/Ocean2ice cruise in the Amundsen Sea in February 2014 (Heywood et al. 2016). In order to include a wide range of conductivity values in the calibration, we chose profiles that encompassed the modified Circumpolar Deep Water, i.e., we chose seal profiles with a maximum temperature > 0 ºC and extending below the pycnocline (depth > 800 m) and compared them with the closest CTD profile. We obtain one scaling factor for conductivity for each seal profile and then calculate the median scaling factor of 1.0018, which we recommend be applied to all seal profiles before calculating the salinity. Longitude and latitude were obtained via ARGOS every time when the seal surface from a dive and then linearly interpolated into continuous time series. Outliers in both salinity and temperature are present within this dataset. We highly recommend that anyone utilising this dataset conduct a thorough visual inspection based TS diagrams and profile plots. We thank Simon Moss for tagging seals with Micheal A Fedak, and Mark Barham, Lars Boehme, Guilherme A Bortolotto for recovering this seal tag. We are grateful to Julia S Wellner for leading the NBP 20-02 cruise (under Thwaites Offshore Research project, THO), and to both Julia S Wellner and Robert D Larter as the PIs of THOR. This dataset was obtained under Ocean2ice (NERC grant NE/J005703/1), TARSAN (NERC grant NE/S006419/1), ARTEMIS (NERC grant NE/W007045/1) and COMPASS (European Research Council Horizon 2020 advanced grant 741120).

The spontaneous formation of zonal jets is a distinctive feature of geostrophic turbulence with the phenomenon witnessed in numerous numerical studies. In such systems, strong rotation anisotropises the spectral evolution of the energy density such that zonal modes are favoured. In physical space, this manifests as eddies zonally elongating and forming into zonal jets. In the presence of large scale dissipation, the flow may reach statistical stationarity such that the zonal structure persists in the zonal and time mean, and is supported by a flux of eddy momentum. What is unclear is how the excitation of Rossby waves arranges the underlying eddy momentum stresses to support the mean flow structures. To study this, we examine a steady-state flow in the so-called ‘zonostrophic’ regime, in which characteristic scales of geostrophic turbulence are well separated and there are several alternating zonal jets that have formed spontaneously. We apply a geometric eddy ellipse formulation, in which momentum fluxes are cast as ellipses that encode information about the magnitude and direction of flux; the latter is described using the tilt angle. With the aid of a zonal filter, it is revealed that the scales responsible for providing the momentum fluxes associated with the jet structure are much smaller than the characteristic scales identified, and occupy a region of the energy spectrum that has been typically associated with isotropic dynamics.

AbstractChlorophyll in phytoplankton absorbs solar radiation (SR) and affects the thermal structure and dynamics within upwelling regions. However, research on this process across global‐scale coastal upwelling systems is still lacking. Here, we use a coupled ocean‐biogeochemical model to investigate differing responses to chlorophyll‐induced solar absorption between Pacific and Atlantic coastal upwelling regions. Chlorophyll‐induced solar absorption leads to colder Pacific coastal upwelling but warmer Atlantic coastal upwelling. In the Pacific, the shading effect of the surface chlorophyll maximum leads to colder subsurface water, which is then upwelled, contributing to cooling. The more stratified upper ocean leads to shallower mixed layer depth, intensifying offshore transport and upwelling. In the Atlantic, the absorption of SR by the subsurface chlorophyll maximum causes warmer and weaker upwelling. The processes described, in turn, trigger positive feedback to ocean biogeochemistry and potentially interact with climate dynamics, underscoring the necessity to incorporate them into Earth system models.

The 18.6-year lunar nodal cycle arises from variations in the angle of the Moon's orbital plane. Previous work has linked the nodal cycle to climate but has been limited by either the length of observations analysed or geographical regions considered in model simulations of the pre-industrial period. Here we examine the global effect of the lunar nodal cycle in multi-centennial climate model simulations of the pre-industrial period. We find cyclic signals in global and regional surface air temperature (with amplitudes of around 0.1 K) and in ocean heat uptake and ocean heat content. The timing of anomalies of global surface air temperature and heat uptake is consistent with the so-called slowdown in global warming in the first decade of the 21st century. The lunar nodal cycle causes variations in mean sea level pressure exceeding 0.5 hPa in the Nordic Seas region, thus affecting the North Atlantic Oscillation during boreal winter. Our results suggest that the contribution of the lunar nodal cycle to global temperature should be negative in the mid-2020s before becoming positive again in the early 2030s, reducing the uncertainty in time at which projected global temperature reaches 1.5 ∘C above pre-industrial levels.

Abstract We investigate feedbacks between subsurface continental shelf ocean temperatures and Antarctic glacial melt using a coupled climate model. The model was forced with SSP5‐8.5 and an uncoupled projection of basal melt and calving fluxes. SSP5‐8.5 forcing with fixed pre‐industrial glacial melt warms all continental shelves, such that historically “cool” and “fresh” shelves transition to “warm.” Additional glacial melt, added at depth, cools the Eastern Ross, Amundsen, and Bellingshausen seas, suggesting a negative feedback on basal melt—a novel result for a coarse resolution coupled model. From the Weddell Sea, along East Antarctica, and into the western Ross Sea—where continental shelves transition to a “warm” state—additional glacial melt increases temperatures at the continental shelf sea floor, suggesting a positive feedback. The sign of the glacial melt–subsurface temperature feedback is critically dependent on continental shelf properties, climate state, and the vertical distribution of glacial melt inputs.

Abstract The Madden–Julian Oscillation (MJO) is the leading mode of sub‐seasonal variability in the tropical atmosphere and is a source of predictability for extratropical weather through its teleconnections. MJO teleconnection patterns can be modulated by the El Niño–Southern Oscillation (ENSO) on seasonal to interannual time scales. However, changes over decadal time scales are less well understood. ERA5 reanalysis data are used to show that the boreal winter MJO teleconnection pattern in the Northern Hemisphere has changed in recent decades in line with changes in the Pacific Decadal Oscillation and Atlantic Multidecadal Variability. Changes are seen in the circulation, temperature and precipitation responses. In particular, from 1997, intraseasonal cold anomalies appear over Europe and the eastern United States due to MJO convection over the western Pacific; these were not present 20 years previously. The decadal variability observed is not the product of aliasing of ENSO modulation of the teleconnection.

Accountability to stakeholders is an important factor for the survival of nonprofit organizations (NPOs). This study extends previous research on other nonprofit categories by examining web-based accountability (WBA) for youth development organizations. The size of the effect of independent variables used in previous studies is determined to be even more significant for youth development organizations than those of other previously studied categories of nonprofits. Organizational density and state generosity index have large effects on WBA, while prosecution and detection indices have medium effects. State ethics score has a small effect on youth organization WBA. Practical implications for both organizations and researchers are discussed, and the effects are also comparable across studies.