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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Aerosol Climate Effects: Local Radiative Forcing and Column Closure Experiments

In an effort to reduce uncertainties in climate change predictions, experiments are being planned and conducted to measure anthropogenic aerosol properties and effects, including effects on radiative fields. The global average, direct anthropogenic aerosol effect on upwelling shortwave fluxes is estimated to be about +1/2 W/sq m, whereas errors in flux changes measured with airborne and spaceborne radiometers are 2 to 8 W/sq m or larger. This poses the question of whether flux changes expected in field experiments will be large enough to measure accurately. This paper obtains a new expression for the aerosol-induced change in upwelling flux, compares it to two-stream and adding-doubling (AD) results, and uses all three methods to estimate expected flux changes. The new expression accounts for the solar zenith angle dependences of aerosol transmission and reflection, as well as of surface albedo, all of which can have a strong effect in determining flux changes measured in field experiments. Despite its relative simplicity, the new expression gives results similar to previous two-stream results. Relative to AD results, it agrees within a few watts per square meter for the intermediate solar elevation angles where the flux changes peak (roughly 10 to 30 degrees), but it has negative errors for higher Sun and positive errors for lower Sun. All three techniques yield aerosol-induced changes in upwelling flux of +8 to +50 W/sq m for aerosol midvisible optical depths of 0.1 to 0.5. Because such aerosol optical depths occur frequently off the U.S. and European Atlantic coasts in summer, the flux changes they induce should be measurable by airborne, and possibly by spaceborne, radiometers, provided sufficient care is taken in experiment design (including measurements to separate aerosol radiative effects from those of absorbing gases). The expected flux changes are about 15 to 100 times larger than the global average flux change expected for the global average anthropogenic sulfate optical depth of 0.04. Reasons for the larger flux changes include the larger optical depths considered here (factor 2.5 to 12), plus restricting the measurements to cloud-free, daytime conditions over the ocean (factor 5 to 9).

Russell, P. B.↗
NASA NTRS2000

BOREAS AFM-1 NOAA/ATDD Long-EZ Aircraft Flux data Over the SSA

This data set contains measurements from the Airborne Flux and Meteorology (AFM)-1 National Oceanographic and Atmospheric Administration/Atmospheric Turbulence and Diffusion Division (NOAA/ATDD) Long-EZ Aircraft collected during the 1994 Intensive Field Campaigns (IFCs) at the southern study area (SSA). These measurements were made from various instruments mounted on the aircraft. The data that were collected include aircraft altitude, wind direction, wind speed, air temperature, potential temperature, water mixing ratio, U and V components of wind velocity, static pressure, surface radiative temperature, downwelling and upwelling total radiation, downwelling and upwelling longwave radiation, net radiation, downwelling and upwelling photosynthectically active radiation (PAR), greenness index, CO2 concentration, O3 concentration, and CH4 concentration. There are also various columns that indicate the standard deviation, skewness, kurtosis, and trend of some of these data. The data are stored in tabular ASCII files. The NOAA/ATDD Long-EZ aircraft flux data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

Crawford, Timothy L.↗
NASA NTRS1999

Mesoscale Variations of Biogeochemical Properties in the Sargasso Sea

A mesoscale resolution biogeochemical survey was carried out in the vicinity of the US Joint Global Ocean Flux Study Bermuda Atlantic Time-Series Study (BATS) site during the summer of 1996. Real-time nowcasting and forecasting of the flow field facilitated adaptive sampling of several eddy features in the area. Variations in upper ocean nutrient and pigment distributions were largely controlled by vertical isopycnal displacements associated with the mesoscale field. Shoaling density surfaces tended to introduce cold, nutrient-rich water into the euphotic zone, while deepening isopycnals displaced nutrient-depleted water downward. Chlorophyll concentration was generally enhanced in the former case and reduced in the latter. Eddy-induced upwelling at the base of the euphotic zone was affected by features of two different types captured in this survey: (1) a typical mid-ocean cyclone in which doming of the main thermocline raised the near-surface stratification upward; and (2) a mode water eddy composed of a thick lens of 18 C water, which pushed up the seasonal thermocline and depressed the main thermocline. Model hindcasts using all available data provide a four-dimensional context in which to interpret temporal trends at the BATS site and two other locations during the two weeks subsequent to the survey. Observed changes in near-surface structure at the BATS site included shoaling iscpycnals, increased nutrient availability at the base of the euphotic zone, and enhanced chlorophyll concentration within the euphotic zone. These trends are explicable in terms of a newly formed cyclone that impinged upon the site during this time period. These observations reveal that eddy upwelling has a demonstrable impact on the way in which the nitrate-density relationship changes with depth from the aphotic zone into the euphotic zone. A similar transition is present in the BATS record, suggesting that eddy-driven upwelling events are present in the time series of upper ocean biogeochemical properties. The variability in main thermocline temperature and nitrate in this synoptic spatial survey spans the range observed in these quantities in the 10-year time series available at BATS to date (1988-1998).

McGillicuddy Dennis J., Jr.↗
NASA NTRS2001

Results of the Second SeaWiFS Data Analysis Round Robin, March 2000 (DARR-00)

The accurate determination of upper ocean apparent optical properties (AOPs) is essential for the vicarious calibration of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) instrument and the validation of the derived data products. To evaluate the importance of data analysis methods upon derived AOP values, the Second Data Analysis Round Robin (DARR-00) activity was planned during the latter half of 1999 and executed during March 2000. The focus of the study was the intercomparison of several standard AOP parameters: (1) the upwelled radiance immediately below the sea surface, L(sub u)(0(-),lambda); (2) the downward irradiance immediately below the sea surface, E(sub d)(0(-),lambda); (3) the diffuse attenuation coefficients from the upwelling radiance and the downward irradiance profiles, L(sub L)(lambda) and K(sub d)(lambda), respectively; (4) the incident solar irradiance immediately above the sea surface, E(sub d)(0(+),lambda); (5) the remote sensing reflectance, R(sub rs)(lambda); (6) the normalized water-leaving radiance, [L(sub W)(lambda)](sub N); (7) the upward irradiance immediately below the sea surface, E(sub u)(0(-)), which is used with the upwelled radiance to derive the nadir Q-factor immediately below the sea surface, Q(sub n)(0(-),lambda); and (8) ancillary parameters like the solar zenith angle, theta, and the total chlorophyll concentration, C(sub Ta), derived from the optical data through statistical algorithms. In the results reported here, different methodologies from three research groups were applied to an identical set of 40 multispectral casts in order to evaluate the degree to which differences in data analysis methods influence AOP estimation, and whether any general improvements can be made. The overall results of DARR-00 are presented in Chapter 1 and the individual methods used by the three groups and their data processors are presented in Chapters 2-4.

Hooker, Stanford B.↗
NASA NTRS1999

Mesoscale Variations of Biogeochemical Properties in the Sargasso Sea

A mesoscale resolution biogeochemical survey was carried out in the vicinity of the U.S. Joint Global Ocean Flux Study Bermuda Atlantic Time-series Study (BATS) site during the summer of 1996. Real-time nowcasting and forecasting of the flow field facilitated adaptive sampling of several eddy features in the area. Variations in upper ocean nutrient and pigment distributions were largely controlled by vertical isopycnal displacements associated with the mesoscale field. Shoaling density surfaces tended to introduce cold, nutrient-rich water into the euphotic zone, while deepening isopycnals displaced nutrient-depleted water downward. Chlorophyll concentration was generally enhanced in the former case and reduced in the latter. Eddy-induced upwelling at the base of the euphotic zone was affected by features of two different types captured in this survey-, (1) a typical mid-ocean cyclone in which doming of the main thermocline raised the near-surface stratification upward and (2) a mode water eddy composed of a thick lens of 18C water, which pushed up the seasonal thermocline and depressed the main thermocline. Model hindcasts using all available data provide a four-dimensional context in which to interpret temporal trends at the BATS site and two other locations during the 2 weeks subsequent to the survey. Observed changes in near-surface structure at the BATS site included shoaling isopycnals, increased nutrient availability at the base of the euphotic zone, and enhanced chlorophyll concentration within the cuphotic zone. These trends are explicable in terms of a newly formed cyclone that impinged upon the site during this time period. These observations reveal that eddy upwelling has a demonstrable impact on the way in which the nitrate-density relationship changes with depth from the aphotic zone into the euphotic zone. A similar transition is present in the BATS record, suggesting that eddy-driven upwelling events are present in the time series of upper ocean biogeochemical properties. The variability in main thermocline temperature and nitrate in this synoptic spatial survey spans the range observed in these quantities in the 10-year time series available at BATS to date (1988-1998).

McGillicuddy, D. J.↗
NASA NTRS1995

Anomalous carbonate precipitates: is the Precambrian the key to the Permian?

Late Permian reefs of the Capitan complex, west Texas; the Magnesian Limestone, England; Chuenmuping reef, south China; and elsewhere contain anomalously large volumes of aragonite and calcite marine cements and sea-floor crusts, as well as abundant microbial precipitates. These components strongly influenced reef growth and may have been responsible for the construction of rigid, open reefal frames in which bryozoans and sponges became encrusted and structurally reinforced. In some cases, such as the upper biostrome of the Magnesian Limestone, precipitated microbialites and inorganic crusts were the primary constituents of the reef core. These microbial and inorganic reefs do not have modern marine counterparts; on the contrary, their textures and genesis are best understood through comparison with the older rock record, particularly that of the early Precambrian. Early Precambrian reefal facies are interpreted to have formed in a stratified ocean with anoxic deep waters enriched in carbonate alkalinity. Upwelling mixed deep and surface waters, resulting in massive seafloor precipitation of aragonite and calcite. During Mesoproterozoic and early Neoproterozoic time, the ocean became more fully oxidized, and seafloor carbonate precipitation was significantly reduced. However, during the late Neoproterozoic, sizeable volumes of deep ocean water once again became anoxic for protracted intervals; the distinctive "cap carbonates" found above Neoproterozoic tillites attest to renewed upwelling of anoxic bottom water enriched in carbonate alkalinity and 12C. Anomalous late Permian seafloor precipitates are interpreted as the product, at least in part, of similar processes. Massive carbonate precipitation was favored by: 1) reduced shelf space for carbonate precipitation, 2) increased flux of Ca to the oceans during increased continental erosion, 3) deep basinal anoxia that generated upwelling waters with elevated alkalinities, and 4) further evolution of ocean water in the restricted Delaware, Zechstein, and other basins. Temporal coincidence of these processes resulted in surface seawater that was greatly supersaturated by Phanerozoic standards and whose only precedents occurred in Precambrian oceans.

Non-NASA Center↗
NASA NTRS2004

Dynamics of the Cold Water Event off the Southeast Coast of the United States in the Summer of 2003: An Application of NASA's Remote Sensing Data to Coastal Studies

The Moderate Resolution Imaging Spectroradiometer (MODIS) instruments onboard of Terra and Aqua satellites provide, for the first time, concurrent measurements of sea surface temperature (SST) and ocean color, which are suitable for coastal upwelling studies. The accuracy, the 1-km spatial resolution, and the almost complete daily coverage of the MODIS data compared with historical measurements make it advantageous for resolving important coastal fronts of chlorophyll concentration and temperature. The cold SST anomaly during summer 2003 off the coast of the South Atlantic Bight is an event that is comprehensively covered by NASA's MODIS and SeaWinds satellite observations. These data combined with in situ tide gauge, mooring, and ship measurements can be used to identify important dynamics responsible for the anomalous cold water event. The analysis of the data suggests that coastal upwelling occurs in the climatological summer forced by the climatological southerlies over the South Atlantic Bight area in summer. However, the strong buoyancy barrier in summer prevents the cold water below the thermocline from reaching the ocean surface. In summer 2003, the southwesterlies in July through August were extraordinarily strong and persistent, which generated the upwelling currents strong enough to overcome the buoyancy resistance. The results of this analysis demonstrate the possibility of monitoring and forecasting the event using combination of the satellite and in situ observations. The MODIS data are archived and distributed by the NASA's Goddard Earth Science (GES) Distributed Active Archive Center (DAAC). The data can be accessed via the URL http://wwv.daac.gsfc.nasa.gov/MODIS.

Yuan, Dongliang↗
NASA NTRS2005

Parga Chasma: Coronae and Rifting on Venus

The majority of coronae (quasicircular volcano-tectonic features) are found along rifts or fracture belts, and the majority of rifts have coronae [e.g. 1,2]. However, the relationship between coronae and rifts remains unclear [3-6]. There is evidence that coronae can form before, after, or synchronously with rifts [3,4]. The extensional fractures in the rift zones have been proposed to be a result of broad scale upwelling and traction on the lower lithosphere [7]. However, not all rift systems have a significant positive geoid anomaly, as would be expected for an upwelling site [8]. This could be explained if the rifts lacking anomalies are no longer active. Coronae are generally accepted to be sites of local upwelling [e.g. 1], but the observed rifting is frequently not radial to the coronae and extends well beyond the coronae into the surrounding plains. Thus the question remains as to whether the rifts represent regional extension, perhaps driven by mantle tractions, or if the coronae themselves create local thinning and extension of the lithosphere. In the first case, a regional extension model should be consistent with the observed characteristics of the rifts. In the latter case, a model of lithospheric loading and fracturing would be more appropriate. A good analogy may be the propagation of oceanic intraplate volcanoes [9].

Smrekar, S. E.↗
NASA NTRS2007

Comparison of Different Global Information Sources Used in Surface Radiative Flux Calculation: Radiative Properties of the Surface

Direct estimates of surface radiative fluxes that resolve regional and weather-scale variabilty over the whole globe with reasonable accuracy have only become possible with the advent of extensive global, mostly satellite, datasets within the past couple of decades. The accuracy of these fluxes, estimated to be about 10-15 W per square meter is largely limited by the accuracy of the input datasets. The leading uncertainties in the surface fluxes are no longer predominantly induced by clouds but are now as much associated with uncertainties in the surface and near-surface atmospheric properties. This study presents a fuller, more quantitative evaluation of the uncertainties for the surface albedo and emissivity and surface skin temperatures by comparing the main available global datasets from the Moderate-Resolution Imaging Spectroradiometer product, the NASA Global Energy and Water Cycle Experiment Surface Radiation Budget project, the European Centre for Medium-Range Weather Forecasts, the National Aeronautics and Space Administration, the National Centers for Environmental Prediction, the International Satellite Cloud Climatology Project (ISCCP), the Laboratoire de Meteorologie Dynamique, NOAA/NASA Pathfinder Advanced Very High Resolution Radiometer project, NOAA Optimum Interpolation Sea Surface Temperature Analysis and the Tropical Rainfall Measuring Mission (TRMM) Microwave Image project. The datasets are, in practice, treated as an ensemble of realizations of the actual climate such that their differences represent an estimate of the uncertainty in their measurements because we do not possess global truth datasets for these quantities. The results are globally representative and may be taken as a generalization of our previous ISCCP-based uncertainty estimates for the input datasets. Surface properties have the primary role in determining the surface upward shortwave (SW) and longwave (LW) flux. From this study, the following conclusions are obtained. Although land surface albedos in the near near-infrared remain poorly constrained (highly uncertain), they do not cause too much error in total surface SW fluxes; the more subtle regional and seasonal variations associated with vegetation and snow are still on doubt. The uncertainty of the broadband black-sky SW albedo for land surface from this study is about 7%, which can easily induce 5-10 W per square meter uncertainty in (upwelling) surface SW flux estimates. Even though available surface (broadband) LW emissivity datasets differ significantly (3%-5% uncertainty), this disagreement is confined to wavelengths greater than 20 micrometers so that there is little practical effect (1-3 W per square meters) on the surface upwelling LW fluxes. The surface skin temperature is one of two leading factors that cause problems with surface LW fluxes. Even though the differences among the various datasets are generally only 2-4 K, this can easily cause 10-15 W per square meter uncertainty in calculated surface (upwelling) LW fluxes. Significant improvements could be obtained for surface LW flux calculations by improving the retrievals of (in order of decreasing importance): (1) surface skin temperature, (2) surface air and near-surface-layer temperature, (3) column precipitable water amount and (4) broadband emissivity. And for surface SW fluxes, improvements could be obtained (excluding improved cloud treatment) by improving the retrievals of (1) aerosols (from our sensitivity studies but not discussed in this work), and (2) surface (black-sky) albedo, of which, NIR part of the spectrum has much larger uncertainty.

Zhang, Yuanchong↗
NASA NTRS2007

Mechanisms Controlling the Interannual Variation of Mixed Layer Temperature Averaged over the Nino-3 Region

The present study examines processes governing the interannual variation of MLT in the eastern equatorial Pacific.Processes controlling the interannual variation of mixed layer temperature (MLT) averaged over the Nino-3 domain (5 deg N-5 deg S, 150 deg-90 deg W) are studied using an ocean data assimilation product that covers the period of 1993-2003. The overall balance is such that surface heat flux opposes the MLT change but horizontal advection and subsurface processes assist the change. Advective tendencies are estimated here as the temperature fluxes through the domain's boundaries, with the boundary temperature referenced to the domain-averaged temperature to remove the dependence on temperature scale. This allows the authors to characterize external advective processes that warm or cool the water within the domain as a whole. The zonal advective tendency is caused primarily by large-scale advection of warm-pool water through the western boundary of the domain. The meridional advective tendency is contributed to mostly by Ekman current advecting large-scale temperature anomalies through the southern boundary of the domain. Unlike many previous studies, the subsurface processes that consist of vertical mixing and entrainment are explicitly evaluated. In particular, a rigorous method to estimate entrainment allows an exact budget closure. The vertical mixing across the mixed layer (ML) base has a contribution in phase with the MLT change. The entrainment tendency due to the temporal change in ML depth is negligible compared to other subsurface processes. The entrainment tendency by vertical advection across the ML base is dominated by large-scale changes in upwelling and the temperature of upwelling water. Tropical instability waves (TIWs) result in smaller-scale vertical advection that warms the domain during La Nina cooling events. However, such a warming tendency is overwhelmed by the cooling tendency associated with the large-scale upwelling by a factor of 2. In summary, all the balance terms are important in the MLT budget except the entrainment due to lateral induction and temporal variation in ML depth. All three advective tendencies are primarily caused by large-scale and low-frequency processes, and they assist the Nino-3 MLT change.

eastern equatorial Pacific↗
NASA NTRS2012

Retrieval of Aerosol Absorption Properties from Satellite Observations

The Angstrom Absorption Exponent (AAE) is a parameter commonly used to characterize the wavelength-dependence of aerosol absorption optical depth (AAOD). It is closely related to aerosol composition. Black carbon (BC) containing aerosols yield AAE values near unity whereas Organic carbon (OC) aerosol particles are associated with values larger than 2. Even larger AAE values have been reported for desert dust aerosol particles. Knowledge of spectral AAOD is necessary for the calculation of direct radiative forcing effect of aerosols and for inferring aerosol composition. We have developed a satellitebased method of determining the spectral AAOD of absorbing aerosols. The technique uses multi-spectral measurements of upwelling radiation from scenes where absorbing aerosols lie above clouds as indicated by the UV Aerosol Index. For those conditions, the satellite measurement can be explained, using an approximations of Beer's Law (BL), as the upwelling reflectance at the cloud top attenuated by the absorption effects of the overlying aerosol layer. The upwelling reflectance at the cloud-top in an aerosol-free atmospheric column is mainly a function of cloud optical depth (COD). In the proposed method of AAE derivation, the first step is determining COD which is retrieved using a previously developed color-ratio based approach. In the second step, corrections for molecular scattering effects are applied to both the observed ad the calculated cloud reflectance terms, and the spectral AAOD is then derived by an inversion of the BL approximation. The proposed technique will be discussed in detail and application results making use of OMI multi-spectral measurements in the UV-Vis. will be presented.

Torres, Omar↗
NASA NTRS2014

Seasonal Variation of Ozone in the Tropical Lower Stratosphere: Southern Tropics are Different from Northern Tropics

We examine the seasonal behavior of ozone by using measurements from various instruments including ozonesondes, Aura Microwave Limb Sounder, and Stratospheric Aerosol and Gas Experiment II. We find that the magnitude of the annual variation in ozone, as a percentage of the mean ozone, exhibits a maximum at or slightly above the tropical tropopause. The maximum is larger in the northern tropics than in the southern tropics, and the annual maximum of ozone in the southern tropics occurs 2 months later than that in the northern tropics, in contrast to usual assumption that the tropics can be treated as a horizontally homogeneous region. The seasonal cycles of ozone and other species in this part of the lower stratosphere result from a combination of the seasonal variation of the Brewer-Dobson circulation and the seasonal variation of tropical and midlatitude mixing. In the Northern Hemisphere, the impacts of upwelling and mixing between the tropics and midlatitudes on ozone are in phase and additive. In the Southern Hemisphere, they are not in phase. We apply a tropical leaky pipe model independently to each hemisphere to examine the relative roles of upwelling and mixing in the northern and southern tropical regions. Reasonable assumptions of the seasonal variation of upwelling and mixing yield a good description of the seasonal magnitude and phase in both the southern and northern tropics. The differences in the tracers and transport between the northern and southern tropical stratospheres suggest that the paradigm of well-mixed tropics needs to be revised to consider latitudinal variations within the tropics.

Mixing↗
DOE OSTI2025

Profiles of Radiative Fluxes at ENA

Profiles of radiative fluxes observed at the Atmospheric Radiation Measurement (ARM)’s Eastern North Atlantic (ENA) observatory along with the ancillary measurements are reported. The below-cloud drizzle properties were derived by combining the data from the ceilometer and Ka-band ARM Zenith Radar (KAZR) following the technique explained by Ghate et al. (2021 JAMC). The cloud and drizzle water path values were derived from the brightness temperatures reported by the microwave radiometer following the technique of Cadeddu et al. (2020 AMT). The cloud water path was then scaled to the KAZR-reported radar reflectivity to calculate profiles of liquid water content (LWC). Following the analysis from Ghate et al. (2023 JGR), cloud droplet effective radius was calculated using the number concentration value of 100 cm-3. The cloud properties, along with the thermodynamic properties, served as an input to the Rapid Radiative Transfer Model (RRTM) to yield profiles of radiative fluxes at a 1-minute temporal and 50-m vertical resolution. The fluxes were then averaged to hourly temporal resolution for analysis. In Mitra et al. (2025 JClim), the calculated profiles were compared against those derived from the satellite measurements (SYN1deg). Flux profiles from the SYN1deg and the thermodynamic and cloud properties used for deriving them are also reported here. Both all-sky and clear-sky radiative flux profiles were calculated. Due to the large data volume, the surface and top-of-atmosphere (TOA) radiative fluxes for the six-year period, and the hourly profiles of the radiative fluxes for January 2018, are submitted here. Full profiles of radiative fluxes calculated from the thermodynamic and cloud properties measured at the ENA site at 1-minute temporal and 50-m vertical resolution for a six-year period are available from the authors. Six files here correspond to the following data: 1_ENARAD_CERES_with_cld_amount_timeseries.nc: Time-series of hourly values of RRTM-simulated values of upwelling and downwelling fluxes at the surface and TOA, observed boundary-layer cloud fractions, and upwelling and downwelling fluxes from the SYN1deg from July 2015 to January 2022. 2_CERES_2018_at_CERES_levels.nc: SYN1deg radiative fluxes at six levels for the year 2018. 3_ENARad_2018_at_CERES_levels.nc: RRTM calculated fluxes at the SYN1deg vertical levels for the year 2018. 4_ENARad_rrtminputs_hourly_201801.nc: Thermodynamic and cloud properties used as an input to the RRTM for January 2018. 5_CERES_inputs_hourly_201801.nc: Thermodynamic and cloud properties utilized by SYN1deg algorithm for January 2018. 6_ENARAD_hourly_201801.nc: Full profiles of hourly averaged radiative fluxes from the RRTM simulations for January 2018.

Atmosphere↗
DOE OSTI2022

Ocean circulation and climate variability in the northern South China Sea during the Greek Minimum derived from coral Δ 14 C and Sr/Ca records

Ocean circulation transports heat, salt and nutrients, and has profound impacts on the marine environment and climate change. However, the seasonal to centennial variations of the paleocirculation of the South China Sea (SCS) and their driving forces are still unclear due to limited records. Here we reconstructed a high-resolution Δ 14 C record of a coral from Sanya to investigate the seasonal variations of the SCS ocean circulation around 2300 cal yr BP during a grand solar minimum (GSM) period. The seasonal Δ 14 C variability shows the influence of coastal upwelling caused by the East Asian Summer Monsoon (EASM) in summer and the effect of water intrusion from the western Pacific Ocean driven by the Kuroshio Intrusion (KI) in winter. Here we compiled the marine radiocarbon reservoir correction (ΔR) records since 2500 cal yr BP, which indicate a gradual decrease of upwelling significantly correlated with the EASM. Comparisons with other climate records suggest that both the EASM and KI may regulate the ocean circulation variability on centennial time scales. As a good index of the sea surface temperature (SST), our Sr/Ca record and spectral analysis results show a low temperature and a low frequency of El Niño-Southern Oscillation (ENSO) events around 2300 cal yr BP. Moreover, the composite coral Sr/Ca-SST and ENSO index records since 2500 cal yr BP show relatively low SST and weak ENSO during GSMs, supporting the modulation of tropical SST and ENSO by solar activity. Our study has provided high-resolution proxy data and revealed the driving forces of ocean circulation and climate change in the SCS at multiple time scales, which should be considered in further modeling work.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Stability of a Mixed–Valence Hydrous Iron–Rich Oxide: Implications for Water Storage and Dynamics in the Deep Lower Mantle

Incorporation of water into mantle compositions can have significant effects on the phase relations in the systems. Here, we synthesized an iron-rich hexagonal hydrous phase (referred to as "HH1-phase") under the high pressure-temperature (P-T) conditions of the deep lower mantle and determined the crystal structure of the HH1-phase at 79 GPa using the multigrain crystallography method. The chemical formula obtained was Fe 12.76 O 18 H x (x ~ to 4.5) in the Fe-O-H system. To demonstrate the role of HH1-phase for water storage in multicomponent systems relevant to mantle compositions, we investigated the stability of HH1-phase in both MgO-rich pyrolitic and SiO 2 -rich basaltic compositions. Our results indicate that the HH1-phase serves as major water storage in a pyrolitic composition, whereas the Al-rich CaCl 2 -type δ-phase and SiO 2 phase are major water storage phases in a SiO 2 -rich basaltic composition. Incorporation of considerable amounts of SiO 2 , MgO, and Al 2 O 3 into the HH1-phase expands its stability field from 98 GPa in the Fe-Al-O-H system to at least 108 GPa (corresponding to similar to 2,400 km depth) in the Mg-Si-Al-Fe-O-H system. Plumes of hot upwelling rock rooted at the base of the lower mantle have been proposed as a possible origin of hotspot volcanoes. The hydrous Fe-rich HH1-phase, if included into the material of upwelling plumes, will decompose on its rising to the upper part of the lower mantle and release water. Our results should provide constraints on water storage in the deep lower mantle and have implications for deep mantle dynamics.

58 GEOSCIENCES↗
DOE OSTI2023

The Impacts of a Weakened Atlantic Meridional Overturning Circulation on ENSO in a Warmer Climate

This study quantifies the impacts of the Atlantic Meridional Overturning Circulation (AMOC) on the El Niño–Southern Oscillation (ENSO) under anthropogenic warming by comparing climate change model simulations with declining and fixed strengths of the overturning. After the 1980s, a weakened AMOC is shown to reduce the strength of the annual cycle of sea surface temperature (SST) in the eastern equatorial Pacific and induce anomalous cross-equatorial northerly winds there, which strengthens ENSO variability by about 11%. An analysis of the Bjerknes stability index reveals that this intensification of ENSO results mainly from enhanced Ekman upwelling feedback due to amplified atmospheric wind response to SST anomalies and oceanic upwelling response to equatorial wind stress anomalies. The weakened AMOC also promotes the occurrence of Central Pacific El Niño events and reduces ENSO skewness. These AMOC impacts on ENSO magnitude and complexity throughout the twenty-first century are however smaller than ENSO variations expected from internal climate variability.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Carbon Outgassing in the Antarctic Circumpolar Current Is Supported by Ekman Transport From the Sea Ice Zone in an Observation‐Based Seasonal Mixed‐Layer Budget

Despite its importance for the global cycling of carbon, there are still large gaps in our understanding of the processes driving annual and seasonal carbon fluxes in the high-latitude Southern Ocean. This is due in part to a historical paucity of observations in this remote, turbulent, and seasonally ice-covered region. Here, we use autonomous biogeochemical float data spanning 6 full seasonal cycles and with circumpolar coverage of the Southern Ocean, complemented by atmospheric reanalysis, to construct a monthly climatology of the mixed layer budget of dissolved inorganic carbon (DIC). We investigate the processes that determine the annual mean and seasonal cycle of DIC fluxes in two different zones of the Southern Ocean—the Sea Ice Zone (SIZ) and Antarctic Southern Zone (ASZ). We find that, annually, mixing with carbon-rich waters at the base of the mixed layer supplies DIC which is, in the ASZ, either used for net biological production or outgassed to the atmosphere. In contrast, in the SIZ, where carbon outgassing and the biological pump are weaker, the surplus of DIC is instead advected northward to the ASZ. In other words, carbon outgassing in the southern Antarctic Circumpolar Current (ACC), which has been attributed to remineralized carbon from deep water upwelled in the ACC, is also due to the wind-driven transport of DIC from the SIZ. These results stem from the first observation-based carbon budget of the circumpolar Southern Ocean and thus provide a useful benchmark to evaluate climate models, which have significant biases in this region.

Sauvé, Jade↗
DOE OSTI2022

Microbial functional diversity across biogeochemical provinces in the central Pacific Ocean

Enzymes catalyze key reactions within Earth’s life-sustaining biogeochemical cycles. Here, we use metaproteomics to examine the enzymatic capabilities of the microbial community (0.2 to 3 µm) along a 5,000-km-long, 1-km-deep transect in the central Pacific Ocean. Eighty-five percent of total protein abundance was of bacterial origin, with Archaea contributing 1.6%. Over 2,000 functional KEGG Ontology (KO) groups were identified, yet only 25 KO groups contributed over half of the protein abundance, simultaneously indicating abundant key functions and a long tail of diverse functions. Vertical attenuation of individual proteins displayed stratification of nutrient transport, carbon utilization, and environmental stress. The microbial community also varied along horizontal scales, shaped by environmental features specific to the oligotrophic North Pacific Subtropical Gyre, the oxygen-depleted Eastern Tropical North Pacific, and nutrient-rich equatorial upwelling. Some of the most abundant proteins were associated with nitrification and C1 metabolisms, with observed interactions between these pathways. The oxidoreductases nitrite oxidoreductase (NxrAB), nitrite reductase (NirK), ammonia monooxygenase (AmoABC), manganese oxidase (MnxG), formate dehydrogenase (FdoGH and FDH), and carbon monoxide dehydrogenase (CoxLM) displayed distributions indicative of biogeochemical status such as oxidative or nutritional stress, with the potential to be more sensitive than chemical sensors. Enzymes that mediate transformations of atmospheric gases like CO, CO 2 , NO, methanethiol, and methylamines were most abundant in the upwelling region. Here, we identified hot spots of biochemical transformation in the central Pacific Ocean, highlighted previously understudied metabolic pathways in the environment, and provided rich empirical data for biogeochemical models critical for forecasting ecosystem response to climate change.

54 ENVIRONMENTAL SCIENCES↗