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Projections of future climate for U.S. national assessments: past, present, future
Climate assessments consolidate our understanding of possible future climate conditions as represented by climate projections, which are largely based on the output of global climate models. Over the past 30 years, the scientific insights gained from climate projections have been refined through model structural improvements, emerging constraints on climate feedbacks, and increased computational efficiency. Within the same period, the process of assessing and evaluating information from climate projections has become more defined and targeted to inform users. As the size and audience of climate assessments has expanded, the framing, relevancy, and accessibility of projections has become increasingly important. This paper reviews the use of climate projections in national climate assessments (NCA) while highlighting challenges and opportunities that have emerged over time. Reflections and lessons learned address the continuous process to understand the broadening assessment audience and evolving user needs. Insights for future NCA development include (1) identifying benchmarks and standards for evaluating downscaled datasets, (2) expanding efforts to gather research gaps and user needs to inform how climate projections are presented in the assessment (3) providing practitioner guidance on the use, interpretation, and reporting of climate projections and uncertainty to better inform decision-making.
Uncertainty quantification of large-eddy simulation results of riverine flows: a field and numerical study
Not provided.
Kuroshio pathways in a climatologically forced model
A high-resolution ocean model forced with an annually repeating atmosphere is used to examine variability of the Kuroshio, the western boundary current in the North Pacific Ocean. A large meander (LM) in the path of the Kuroshio south of Japan develops and disappears in a highly bimodal fashion on decadal timescales. The modeled meander is comparable in timing and spatial extent to an observed feature in the region. Various characteristics of the LM are examined, including relative vorticity, transport, and velocity shear. The many similarities between the model and observations indicate that the meander results from intrinsic oceanic variability, which is represented in this climatologically forced model. Each LM is preceded by a smaller “trigger” meander that originates at the south end of Kyushu, moves up the coast, and develops into the LM. However, there are also many meanders very similar in character to the trigger meander that do not develop into LMs. Formation of an LM only occurs when a deep anticyclone associated with the trigger meander forms near Koshu Seamount. Furthermore, the major axis of that deep anticyclone must be oriented away from the coast, rather than alongshore. In the specific case of interaction of a trigger meander with a deep anticyclone with major axis oriented away from the coastline, LM formation occurs.
Sea-surface temperature in relation to air temperature in the Gulf of St. Lawrence: Interdecadal variability and long term trends
Monthly average sea-surface temperatures (SST) derived from NOAA-AVHRR remote sensing data are analyzed for the period 1982–2011 for the Gulf of St. Lawrence (Canada) and compared to monthly average air temperature. Results show that SST increased by 1 to 1.5 °C during the period when averaging from May to November of each year, a change associated with interdecadal variability rather than a long term trend. SST averaged over the ice-free months of May–November is strongly correlated to an index of the April–November air temperature anomaly, capturing up to 90% of the variance, suggesting strong coupling between air and sea-surface temperatures on seasonal time scales. The air temperature anomaly index series can be used as a proxy for longer term climate variability of SST prior to 1982. Overall warming trends in air temperature of 0.9 °C and 0.6 °C per century were found using data from weather stations dating back to 1873 and from the National Centers for Environmental Prediction (NCEP) reanalysis that goes back to 1871. The strong co-variations of SST and air temperature indicate that the SST has likely increased by a similar amount. These co-variations will help to predict the response of the Gulf water temperature to changing climate as well as provide a perspective with respect to changes that have occurred in the previous century.
A comparison of North Pacific and North Atlantic subtropical mode waters in a climatologically-forced model
Subtropical mode water (STMW), a water mass with homogeneous temperature and density and low potential vorticity, is formed in the subtropical gyres of both the North Pacific and North Atlantic Oceans. In the North Atlantic, this water mass is known as Eighteen Degree Water (EDW), while the corresponding water mass in the Pacific is identified as North Pacific Subtropical Mode Water (NPSTMW). This analysis compares properties of EDW with NPSTMW as well as the intrinsic oceanic variability of both, within the framework of a high resolution model with climatological atmospheric forcing. Interannual variability is evident in both volume and characteristics of EDW and NPSTMW, but the magnitude of variability is small, indicating that observed variability is largely forced by atmospheric changes. Volume of EDW is greater than volume of NPSTMW, but volume variability is similar in the two basins, and is dominated by the seasonal cycle in both cases. The most significant differences are found in the average ages of EDW compared to NPSTMW. Although the volume of STMW formed in each basin is similar, different circulation patterns lead to a higher average age in the North Atlantic, as EDW is more likely to be advected away from the formation region and remain subducted in the North Atlantic, while NPSTMW is more likely to be reventilated the following winter in the North Pacific.
Record-breaking 2020 summer marine heatwaves in the western North Pacific
Record-breaking marine heatwaves (MHWs) occurred in the western North Pacific during the summer of 2020. These unprecedented MHWs were consistent with favorable large-scale conditions that are linked to an anomalous western North Pacific subtropical high (WNPSH), resulting mainly from sea surface temperature (SST) anomalies across the tropical oceans. In addition, a moderate La Niña-like pattern was also conducive to transporting warm seawater to the western North Pacific. Mixed-layer heat budgets suggest that surface heat flux contributed to the SST anomaly in the western subtropical Pacific. In contrast, oceanic heat advection dominanted in the South China Sea and the western equatorial Pacific. Numerical model experiments indicated that the tropical Indian Ocean SST anomalies were responsible for the enhanced WNPSH. The increased zonal SST gradient across the tropical Pacific also played an important role. Inter-ocean interactions can modulate climate variability through ocean-atmospheric coupling and deserve more attention when predicting MHWs within the context of global warming. Additionally, it is critical to consider MHWs as a powerful tool in detecting acute, intense thermal stress events in the coral bleaching pre-warning system.
Impacts of climate change on estuarine stratification and implications for hypoxia within a shallow subtropical system
Vertical density stratification often plays an important role in the formation and expansion of coastal hypoxic zones through its effect on near-bed circulation and vertical oxygen flux. However, the impact of future climate change on estuarine circulation is widely unknown. Here, we developed and calibrated a three-dimensional hydrodynamic model for Pensacola Bay, a shallow subtropical estuary in the northeastern Gulf of Mexico. Model simulations based on years 2013–2017 were applied to examine changes in salinity, temperature, and density under future climate scenarios, including increased radiative forcing (IR) and temperature (T), increased freshwater discharge (D), sea level rise (SLR), and wind intensification (W). Simulations showed that the impacts of climate change on modeled state variables varied over time with external forcing conditions. The model demonstrated the potential for sea level rise and increased freshwater discharge to episodically increase vertical density gradients in the Bay. However, increased wind forcing destabilized vertical gradients, at times reducing the spatial extent and duration of stable stratification. For time periods with low freshwater discharge, moderate increases in wind speed (10%) can destabilize density gradients strengthened by increased discharge (10%) and sea level rise (0.48 m). In contrast, destruction of strong density gradients that form near the mid-Bay channel following flood events requires stronger wind forcing. Furthermore, these results highlight the importance of considering natural variability in freshwater and wind forcing, as well as local phenomena that are generally unresolved by global climate models.
Drake passage and central american seaway controls on the distribution of the oceanic carbon reservoir
A coupled carbon/climate model is used to explore the impact of Drake Passage opening and Central American Seaway closure on the distribution of carbon in the global oceans. We find that gateway evolution likely played an important role in setting the modern day distribution of oceanic dissolved inorganic carbon (DIC), which is currently characterized by relatively low concentrations in the Atlantic ocean, and high concentrations in the Southern, Indian, and Pacific oceans. In agreement with previous studies, we find a closed Drake Passage in the presence of an open Central American Seaway results in suppressed Atlantic meridional overturning and enhanced southern hemispheric deep convection. Opening of the Drake Passage triggers Antarctic Circumpolar Current flow and a weak Atlantic meridional overturning circulation (AMOC). Subsequent Central American Seaway closure reinforces the AMOC while also stagnating equatorial Pacific subsurface waters. These gateway-derived oceanographic changes are reflected in large shifts to the global distribution of DIC. An initially closed Drake Passage results in high DIC concentrations in the Atlantic and Arctic oceans, and lower DIC concentrations in the Pacific/Indian/Southern oceans. Opening Drake Passage reverses this gradient by lowering mid-depth Atlantic and Arctic DIC concentrations and raising deep Pacific/Indian/Southern Ocean DIC concentrations. Central American Seaway closure further reinforces this trend through additional Atlantic mid-depth DIC decreases, as well as Pacific mid-depth DIC concentration increases, with the net effect being a transition to a modern distribution of oceanic DIC.
Virioplankton assemblages from challenger deep, the deepest place in the oceans
Hadal ocean biosphere, that is, the deepest part of the world’s oceans, harbors a unique microbial community, suggesting a potential uncovered co-occurring virioplankton assemblage. Herein, we reveal the unique virioplankton assemblages of the Challenger Deep, comprising 95,813 non-redundant viral contigs from the surface to the hadal zone. Almost all of the dominant viral contigs in the hadal zone were unclassified, potentially related to Alteromonadales and Oceanospirillales. 2,586 viral auxiliary metabolic genes from 132 different KEGG orthologous groups were mainly related to the carbon, nitrogen, sulfur, and arsenic metabolism. Lysogenic viral production and integrase genes were augmented in the hadal zone, suggesting the prevalence of viral lysogenic life strategy. Abundant rve genes in the hadal zone, which function as transposase in the caudoviruses, further suggest the prevalence of viral-mediated horizontal gene transfer. This study provides fundamental insights into the virioplankton assemblages of the hadal zone, reinforcing the necessity of incorporating virioplankton into the hadal biogeochemical cycles.
Benthic storms, nepheloid layers, and linkage with upper ocean dynamics in the western North Atlantic
Benthic storms are episodic periods of strong abyssal currents and intense, benthic nepheloid (turbid) layer development. In order to interpret the driving forces that create and sustain these storms, we synthesize measurements of deep ocean currents, nephelometer-based particulate matter (PM) concentrations, and seafloor time-series photographs collected during several science programs that spanned two decades in the western North Atlantic. Benthic storms occurred in areas with high sea-surface eddy kinetic energy, and they most frequently occurred beneath the meandering Gulf Stream or its associated rings, which generate deep cyclones, anticyclones, and/or topographic waves; these create currents with sufficient bed-shear stress to erode and resuspend sediment, thus initiating or enhancing benthic storms. Occasionally, strong currents do not correspond with large increases in PM concentrations, suggesting that easily erodible sediment was previously swept away. Periods of moderate to low currents associated with high PM concentrations are also observed; these are interpreted as advection of PM delivered as storm tails from distal storm events. Outside of areas with high surface and deep eddy kinetic energy, benthic nepheloid layers are weak to non-existent, indicating that benthic storms are necessary to create and maintain strong nepheloid layers. Origins and intensities of benthic storms are best identified using a combination of time-series measurements of bottom currents, PM concentration, and bottom photographs, and these should be coupled with water-column and surface-circulation data to better interpret the specific relations between shallow and deep circulation patterns. Understanding the generation of benthic nepheloid layers is necessary in order to properly interpret PM distribution and its influence on global biogeochemistry.
Nuclear Structure and Decay Data for A=220 Isobars
Here, this work presents a comprehensive and critical evaluation of experimental nuclear spectroscopic data from reactions and decays for all 11 known nuclides with mass number A=220 (Pb, Bi, Po, At, Rn, Fr, Ra, Ac, Th, Pa, and Np). Recommended values are produced for level energies, spins and parities, half-lives, and radiation properties including energies, branching ratios, and multipolarities of γ rays, as well as characteristics of β and α radiation decays, based on all available experimental data. This work supersedes previous A=220 evaluations: 2011Br05, 1997Ar04, 1986Ma45, 1976El04.