Today, ocean circulation is characterized by southward-flowing North Atlantic Deep Water and northward-flowing Antarctic Bottom Water, with a mixture of water masses filling the Pacific and Indian Oceans. Also, a Southern Hemisphere supergyre (i.e., an inter-basin wind-driven current) facilitates exchange of water among South Pacific, Indian, and South Atlantic Oceans subtropical gyres. The ocean circulation in the Eocene was different. Here we present new benthic foraminiferal oxygen and carbon stable isotopes (delta O-18(bf) and delta C-13(bf)) from Ocean Drilling Program (ODP) Site 1090 (Agulhas Ridge) spanning the middle and early late Eocene that extend a published late Eocene-early Oligocene record (Pusz et al., 2011, https://doi.org/10.1029/2010pa001950) into a time characterized by the evolution of the Drake Passage and Tasman Gateway. The comparison of the Site 1090 combined data set with delta O-18(bf) and delta C-13(bf) from the Southern, Atlantic, and sub-Antarctic Indian Oceans confirms the presence of a water mass with higher delta O-18(bf) at depths <2,000 m and a water mass with lower delta O-18(bf) at depths >2,000 m, as already reported. We interpret these signals to be evidence of a deep supergyre at depths <2,000 m transporting salty higher delta O-18(bf) waters originating from the Indian Ocean into the Southern and eastern South Atlantic Oceans. Cold waters that formed around Antarctica spread northward, bathing sites >2,000 m. As the Drake Passage and Tasman Gateways opened and deepened and the Antarctic Circumpolar Current developed, deep-water formation became more prominent at higher latitudes, while the supergyre became restricted to shallower depths.
An explicit charging scheme was added to the WRF spectral (bin) microphysics (SBM) scheme and compared with the well-tested NSSL bulk microphysics/electrification scheme. The overall approach is a hybrid one because bin-by-bin charges are integrated over the volume of each grid point and then coupled with the electric field generator and discharge scheme within the WRF-ELEC Model. The explicit charging and coupled model were used to simulate a previously studied U.S. continental squall line. Including inductive charging in addition to noninductive charging led to an increase in the relative number of positive discharges compared to negative discharges. Different aerosol concentrations were tested to assess charging sensitivity to aerosol type and size distribution. More lightning events were produced when aerosols were continental, while far less were produced with a simulation with maritime aerosols. SBM simulations produced more cloud-to-ground lightning than the NSSL bulk microphysical scheme, but the number of cloud-to-ground simulated events in both the SBM and NSSL simulations was much smaller than in observations. An SBM sensitivity test with "relaxed" charging constraints produced a greater number of cloud-to-ground events, closer to observed values. The general agreement between the SBM and NSSL in charge structure and lightning production suggests a similarly complete implementation of charge processes. Newly implemented features for both schemes are the calculation of energy discharged per lightning event and the subdivision of the time step for the sedimentation process to prevent the development of excessive electric field magnitudes on large dynamic time steps. SIGNIFICANCE STATEMENT: This study advances weather research and forecasting by integrating a detailed cloud electrification mechanism into a widely used weather model. It reveals how different charging processes and aerosol pollution influence lightning intensity, frequency, and discharge energy, highlighting the role of air quality in storm electrification. The new model improves predictions of lightning patterns by considering the behavior of cloud-ice particles and their fall speeds, while more frequent calculations of lightning discharges prevent the development of excessive electric fields. Although, in this initial test, it underestimates cloud-to-ground lightning compared to observations, the model aligns well with the standard approach, suggesting consistent treatment of charge processes. These findings deepen our understanding of storm electrification and emphasize the need for further refinement to enhance lightning forecasting accuracy.
Surface mixed-layer dynamics play a crucial role in modulating the climate as it is the oceanic layer that directly communicates with the atmosphere. The resolution of global ocean models is, however, often restricted to ; this is too coarse to adequately resolve mixed-layer processes, and we depend on parametrizations. One of such parametrizations is the mixed-layer eddy (MLE) parametrization. Here, we compare the performance of two MLE parametrizations [Fox-Kemper et al. (2011, https://doi.org/10.1016/j.ocemod.2010.09.002 hereon BFF11) and Bodner et al. (2023, https://doi.org/10.1175/jpo-d-21-0297.1 hereon BOD23)], and document their impact in three global ocean simulations. Upon tuning, and diagnosing submesoscale-permitting truth simulations, the MLE efficiency coefficient in BOD23 ranges between the values of 0.003-0.038, while 0.06 to 0.07 for BFF11. We find that the spatial distribution of mixed-layer depth and ventilation of the abyssal ocean, using the ideal-age tracer and Atlantic Meridional Overturning Circulation as its proxy, are sensitive to the interaction between MLE parametrizations and ocean surface boundary-layer mixing schemes.
Equatorial upwelling plays a crucial role in regulating regional climate variability and biological productivity from seasonal to interannual time scales. Typically, sea surface temperature or surface chlorophyll anomalies are used as proxies for upwelling because of the challenges in directly measuring vertical velocities. Here, we show that using a synthesis product of surface drifter observations, reanalysis winds, and satellite altimetry to infer vertical velocity in the equatorial band (+/- 3 degrees; w eq) improves the representation of the spatiotemporal characteristics of w eq compared to estimates from other commonly used products. We focus on the annual mean, seasonal cycle, interannual variations, and long-term trends of vertical velocity estimates, derived by applying the continuity equation to horizontal current divergence in the upper 30 m across the tropical Pacific, Atlantic, and Indian Oceans. Mean w eq values of 0.6 +/- 0.2, 0.3 +/- 0.2 and 0.1 +/- 0.2 m day-1 are observed in the Pacific (150 degrees W-90 degrees W), Atlantic (20 degrees W-0 degrees), and Indian Ocean (60 degrees E-90 degrees E), respectively. Vertical transport across 30 m is 46 +/- 14 Sv in the Pacific and 8 +/- 4 Sv in the Atlantic. Interannual variations in w eq are primarily driven by climate modes specific to each basin and are up to +/- 0.4 m day-1 in the Pacific, +/- 0.1 m day-1 in the Atlantic, and up to +/- 0.6 m day-1 in the Indian Ocean. From 1993 to 2022, Pacific w eq significantly increased by 24 +/- 13% (0.14 +/- 0.07 m day-1). This increase in Pacific equatorial upwelling aligns with stronger trade winds and intensified upper-ocean currents.
Communication allows social species to exchange information among group members. In aquatic environments, acoustic signals are among the most effective forms of communication and are important for many species, including cetaceans. Beluga whales (Delphinapterus leucas) are highly social and vocal, yet little is known about the functionality of their social calls. To examine context-dependent vocal behavior in belugas, we collected passive acoustic data and fine-scale behavioral observations for the endangered Cook Inlet beluga population. The resulting dataset includes 1,720 annotated vocalizations collected over 21 behaviorally encoded encounters. We fit generalized linear mixed models to these data to investigate the effect of behavioral state, group size, calf presence, and tidal state on (1) calling rate (number of calls/minute) and (2) call category (whistles, pulsed calls, combined calls). Belugas were more likely to call when traveling and had higher calling rates during flood tides. Group-level calling rate increased sublinearly with group size, suggesting that individuals called less in larger groups, possibly reflecting increased listening, vocal coordination, or a strategy to avoid acoustic masking. Group calling rate increased before transitions between traveling and milling, suggesting a possible link between communication and behavioral transitions. Whistles were more prevalent when traveling, while pulsed calls were more prevalent when milling. Combined calls occurred only when calves were present, indicating the importance of these calls in communication with calves. Identifying these communication patterns and the contexts in which they occur can enhance our understanding of beluga whale ecology and aid in conservation efforts via passive acoustic monitoring. We provide the first description of the behavioral, social, and environmental factors associated with vocal communication in an Alaskan beluga whale population. Cook Inlet beluga whales (CIB) exhibit context-dependent shifts in vocal activity as a function of behavior, tidal state, and group size. CIB use whistles while traveling, pulsed calls while milling, and only produce combined calls when calves are present. Additionally, calling rate appeared to increase prior to behavioral transitions in a small number of observed encounters. These patterns may be related to the types of information being transmitted in these specific contexts, as well as aid in the coordination of group dynamics. Understanding these factors not only advances knowledge of beluga communication, and animal communication more generally, but also contributes to the development of passive acoustic methods to monitor habitat use, behavior, and group characteristics.
