River effects on sea-level rise in the Río de la Plata estuary during the past century

Identifying the causes for historical sea-level changes in coastal tide-gauge records is important for constraining oceanographic, geologic, and climatic processes. The Río de la Plata estuary in South America features the longest tide-gauge records in the South Atlantic. Despite the relevance of these data for large-scale circulation and climate studies, the mechanisms underlying relative sea-level changes in this region during the past century have not been firmly established. I study annual data from tide gauges in the Río de la Plata and stream gauges along the Río Paraná and Río Uruguay to establish relationships between river streamflow and sea level over 1931–2014. Regression analysis suggests that streamflow explains 59 %±17 % of the total sea-level variance at Buenos Aires, Argentina, and 28 %±21 % at Montevideo, Uruguay (95 % confidence intervals). A long-term streamflow increase effected sea-level trends of 0.71±0.35 mm yr−1 at Buenos Aires and 0.48±0.38 mm yr−1 at Montevideo. More generally, sea level at Buenos Aires and Montevideo respectively rises by (7.3±1.8)×10-6 m and (4.7±2.6)×10-6 m per 1 m3 s−1 streamflow increase. These observational results are consistent with simple theories for the coastal sea-level response to streamflow forcing, suggesting a causal relationship between streamflow and sea level mediated by ocean dynamics. Findings advance understanding of local, regional, and global sea-level changes; clarify sea-level physics; inform future projections of coastal sea level and the interpretation of satellite data and proxy reconstructions; and highlight future research directions. Specifically, local and regional river effects should be accounted for in basin-scale and global mean sea-level budgets as well as reconstructions based on sparse tide-gauge records.</p

A Note on Practical Evaluation of Budgets in ECCO Version 4 Release 3

An outline and technical description is provided for evaluating tracer budgets (heat, salt, volume) offline using available monthly ECCOv4 model diagnostic output. Methods described here are intended for analysis of model output on its native spatial grid.NASA, NS

Likely weakening of the Florida Current during the past century revealed by sea-level observations

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Piecuch, C. G. Likely weakening of the Florida Current during the past century revealed by sea-level observations. Nature Communications, 11(1), (2020): 3973, doi:10.1038/s41467-020-17761-w.The Florida Current marks the beginning of the Gulf Stream at Florida Straits, and plays an important role in climate. Nearly continuous measurements of Florida Current transport are available at 27°N since 1982. These data are too short for assessing possible multidecadal or centennial trends. Here I reconstruct Florida Current transport during 1909–2018 using probabilistic methods and principles of ocean physics applied to the available transport data and longer coastal sea-level records. Florida Current transport likely declined steadily during the past century. Transport since 1982 has likely been weaker on average than during 1909–1981. The weakest decadal-mean transport in the last 110 y likely took place in the past two decades. Results corroborate hypotheses that the deep branch of the overturning circulation declined over the recent past, and support relationships observed in climate models between the overturning and surface western boundary current transports at multidecadal and longer timescales.Funding came from NSF awards OCE-1558966 and OCE-1834739. I acknowledge helpful conversations with M. Andres, L. Beal, S. Coats, S. Dangendorf, S. Elipot, T. Frederikse, N. Foukal, G. Gawarkiewicz, G. Gebbie, B. Hamlington, J. Heiderich, A. Kemp, Y.-O. Kwon, F. Landerer, C. Little, M. Thomas, T. Wahl, and S. Wijffels

Mechanisms controlling global mean sea surface temperature determined from a state estimate

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 45 (2018): 3221-3227, doi:10.1002/2017GL076821.Global mean sea surface temperature ((T) over bar) is a variable of primary interest in studies of climate variability and change. The temporal evolution of (T) over bar) can be influenced by surface heat fluxes ((F) over bar)) and by diffusion ((D) over bar)) and advection ((A) over bar)) processes internal to the ocean, but quantifying the contribution of these different factors from data alone is prone to substantial uncertainties. Here we derive a closed (T) over bar) budget for the period 1993-2015 based on a global ocean state estimate, which is an exact solution of a general circulation model constrained to most extant ocean observations through advanced optimization methods. The estimated average temperature of the top (10-m thick) level in the model, taken to represent (T) over bar), shows relatively small variability at most time scales compared to (F) over bar), (D) over bar), or (A) over bar), reflecting the tendency for largely balancing effects from all the latter terms. The seasonal cycle in (T) over bar) is mostly determined by small imbalances between (F) over bar) and (D) over bar), with negligible contributions from (A) over bar). While (D) over bar) seems to simply damp (F) over bar) at the annual period, a different dynamical role for (D) over bar) at semiannual period is suggested by it being larger than (F) over bar). At periods longer than annual, (A) over bar) contributes importantly to (T) over bar) variability, pointing to the direct influence of the variable ocean circulation on (T) over bar) and mean surface climate. Plain Language Summary Global mean sea surface temperature (T) over bar) is a key metric when defining the Earth's climate. Determining what controls the evolution of (T) over bar )T is thus vital for understanding past climate variability and predicting its future evolution. Processes that control (T) over bar) involve forcing surface heat fluxes, as well as advection and diffusion of heat internal to the ocean, but their relative contributions are poorly known and difficult to assess from observations alone. Here we use advanced methods to combine models and data and derive a closed budget for (T) over bar) variability in terms of the forcing, advection, and diffusion processes. The estimated (T) over bar) shows relatively small variability compared to surface forcing, advection, or diffusion, reflecting the tendency for largely balancing effects from all the latter terms. The seasonal cycle in (T) over bar) is mostly determined by small imbalances between forcing and diffusion, with negligible contributions from advection. Diffusion does not always act as a simple damping of forcing surface fluxes, however. In addition, at periods longer than annual, advection contributes importantly to (T) over bar) variability. The results point to the direct influence of the variable ocean circulation on (T) over bar) and the Earth's surface climate.NSF Grant Number: PLR-15133962018-09-2

Intraseasonal sea level variability in the Persian Gulf

Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 51(5), (2021): 1687–1704, https://doi.org/10.1175/JPO-D-20-0296.1.Satellite observations are used to establish the dominant magnitudes, scales, and mechanisms of intraseasonal variability in ocean dynamic sea level (ζ) in the Persian Gulf over 2002–15. Empirical orthogonal function (EOF) analysis applied to altimetry data reveals a basinwide, single-signed intraseasonal fluctuation that contributes importantly to ζ variance in the Persian Gulf at monthly to decadal time scales. An EOF analysis of Gravity Recovery and Climate Experiment (GRACE) observations over the same period returns a similar large-scale mode of intraseasonal variability, suggesting that the basinwide intraseasonal ζ variation has a predominantly barotropic nature. A linear barotropic theory is developed to interpret the data. The theory represents Persian Gulf average ζ (¯ζ) in terms of local freshwater flux, barometric pressure, and wind stress forcing, as well as ζ at the boundary in the Gulf of Oman. The theory is tested using a multiple linear regression with these freshwater flux, barometric pressure, wind stress, and boundary ζ quantities as input and ¯ζ as output. The regression explains 70% ± 9% (95% confidence interval) of the intraseasonal ¯ζ variance. Numerical values of regression coefficients computed empirically from the data are consistent with theoretical expectations from first principles. Results point to a substantial nonisostatic response to surface loading. The Gulf of Oman ζ boundary condition shows lagged correlation with ζ upstream along the Indian subcontinent, Maritime Continent, and equatorial Indian Ocean, suggesting a large-scale Indian Ocean influence on intraseasonal ¯ζ variation mediated by coastal and equatorial waves and hinting at potential predictability. This study highlights the value of GRACE for understanding sea level in an understudied marginal sea.The authors acknowledge support from NASA through the Sea Level Change Team (Grant 80NSSC20K1241) and GRACE Follow-On Science Team (Grant 80NSSC20K0728). The authors appreciate comments from two anonymous reviewers that improved the manuscript

Meridional asymmetry in recent decadal sea-level trends in the subtropical Pacific Ocean

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Schloesser, F., Thompson, P. R., & Piecuch, C. G. Meridional asymmetry in recent decadal sea-level trends in the subtropical Pacific Ocean. Geophysical Research Letters, 48(6), (2021): e2020GL091959, https://doi.org/10.1029/2020GL091959.Recent sea surface height (SSH) trends in the South Pacific are substantially greater than trends in the North Pacific. Here, we use the Estimating the Climate and Circulation of the Ocean Version 4 Release 4 ocean state estimate and the Ocean Reanalysis System 5 to identify the forcing and mechanisms underlying that meridional asymmetry during 2005–2015. Thermosteric contributions dominate the spatial structure in Pacific SSH trends, but contributions from local surface heat fluxes are small. Wind stress trends drive a spin-up of the South Pacific subtropical gyre and a northward shift of the North Pacific subtropical gyre. A reduced gravity model forced with reanalysis winds qualitatively reproduces the meridional seesaw in sea level, suggesting that asymmetric trends in subtropical wind stress drive a cross-equatorial heat transport. A reversal in forcing associated with this process could impact near-term rates of coastal sea-level change, particularly in Pacific Island communities.F. Schloesser and P. R. Thompson were supported by NASA grant 80NSSC17K0564 and NSF grant 1558980. C. G. Piecuch was supported by the NASA Sea Level Change Team (grant 80NSSC20K1241)

How is New England coastal sea level related to the Atlantic meridional overturning circulation at 26 degrees N?

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters, 46(10), (2019): 5351-5360, doi: 10.1029/2019GL083073.Monthly observations are used to study the relationship between the Atlantic meridional overturning circulation (AMOC) at 26° N and sea level (ζ) on the New England coast (northeastern United States) over nonseasonal timescales during 2004–2017. Variability in ζ is anticorrelated with AMOC on intraseasonal and interannual timescales. This anticorrelation reflects the stronger underlying antiphase relationship between ageostrophic Ekman‐related AMOC transports due to local zonal winds across 26° N and ζ changes arising from local wind and pressure forcing along the coast. These distinct local atmospheric variations across 26° N and along coastal New England are temporally correlated with one another on account of large‐scale atmospheric teleconnection patterns. Geostrophic AMOC contributions from the Gulf Stream through the Florida Straits and upper‐mid‐ocean transport across the basin are together uncorrelated with ζ. This interpretation contrasts with past studies that understood ζ and AMOC as being in geostrophic balance with one another.This work was supported by NSF awards OCE‐1558966, OCE‐1834739, and OCE‐1805029; NASA contract NNH16CT01C; and the J. Lamar Worzel Assistant Scientist Fund and the Penzance Endowed Fund in Support of Assistant Scientists at the Woods Hole Oceanographic Institution. Helpful comments from Magdalena Andres and two anonymous reviewers are acknowledged. Tide‐gauge sea level data were provided by the Permanent Service for Mean Sea Level (www.psmsl.org). Observations of the overturning circulation were taken from the RAPID data download page (www.rapid.ac.uk/data.php). Time series of the North Atlantic Oscillation and Arctic Oscillation were downloaded from the National Oceanic and Atmospheric Administration Earth System Research Laboratory Physical Sciences Division website (www.esrl.noaa.gov/psd/). Reanalysis wind stress and air pressure fields were provided by the Community Storage Server at Woods Hole Oceanographic Institution (http://cmip5.whoi.edu/).2019-11-0

Low-frequency dynamic ocean response to barometric-pressure loading

Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(11), (2022): 2627-2641, https://doi.org/10.1175/jpo-d-22-0090.1.Changes in dynamic manometric sea level ζm represent mass-related sea level changes associated with ocean circulation and climate. We use twin model experiments to quantify magnitudes and spatiotemporal scales of ζm variability caused by barometric pressure pa loading at long periods (≳1 month) and large scales (≳300km) relevant to Gravity Recovery and Climate Experiment (GRACE) ocean data. Loading by pa drives basin-scale monthly ζm variability with magnitudes as large as a few centimeters. Largest ζm signals occur over abyssal plains, on the shelf, and in marginal seas. Correlation patterns of modeled ζm are determined by continental coasts and H/f contours (H is ocean depth and f is Coriolis parameter). On average, ζm signals forced by pa represent departures of ≲10% and ≲1% from the inverted-barometer effect ζib on monthly and annual periods, respectively. Basic magnitudes, spatial patterns, and spectral behaviors of ζm from the model are consistent with scaling arguments from barotropic potential vorticity conservation. We also compare ζm from the model driven by pa to ζm from GRACE observations. Modeled and observed ζm are significantly correlated across parts of the tropical and extratropical oceans, on shelf and slope regions, and in marginal seas. Ratios of modeled to observed ζm magnitudes are as large as ∼0.2 (largest in the Arctic Ocean) and qualitatively agree with analytical theory for the gain of the transfer function between ζm forced by pa and wind stress. Results demonstrate that pa loading is a secondary but nevertheless important contributor to monthly mass variability from GRACE over the ocean.The authors acknowledge support from the National Aeronautics and Space Administration through the GRACE Follow-On Science Team (Grant 80NSSC20K0728) and the Sea Level Change Team (Grant 80NSSC20K1241). The contribution from I. F. and O. W. represents research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (Grant 80NM0018D0004)

High-Tide Floods and Storm Surges During Atmospheric Rivers on the US West Coast

Amospheric rivers (ARs) effect inland hydrological impacts related to extreme precipitation. However, little is known about the possible coastal hazards associated with these storms. Here we elucidate high-tide floods (HTFs) and storm surges during ARs through a statistical analysis of data from the US West Coast during 1980-2016. HTFs and landfalling ARs co-occur more often than expected from random chance. Between 10%-63% of HTFs coincide with landfalling ARs, depending on location. However, only 2%-15% of ARs coincide with HTFs, suggesting that ARs typically must co-occur with anomalously high tides or mean sea levels to cause HTFs. Storm surges during ARs are interpretable in terms of local wind, pressure, and precipitation forcing. Meridional wind and barometric pressure are the primary drivers of the storm surge. This study highlights the relevance of ARs to coastal impacts, clarifies the drivers of storm surge during ARs, and identifies future research directions

Local and remote forcing of interannual sea‐level variability at Nantucket Island

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wang, O., Lee, T., Piecuch, C., Fukumori, I., Fenty, I., Frederikse, T., Menemenlis, D., Ponte, R., & Zhang, H. Local and remote forcing of interannual sea‐level variability at Nantucket Island. Journal of Geophysical Research: Oceans, 127(6), (2022): e2021JC018275, https://doi.org/10.1029/2021jc018275.The relative contributions of local and remote wind stress and air-sea buoyancy forcing to sea-level variations along the East Coast of the United States are not well quantified, hindering the understanding of sea-level predictability there. Here, we use an adjoint sensitivity analysis together with an Estimating the Circulation and Climate of the Ocean (ECCO) ocean state estimate to establish the causality of interannual variations in Nantucket dynamic sea level. Wind forcing explains 67% of the Nantucket interannual sea-level variance, while wind and buoyancy forcing together explain 97% of the variance. Wind stress contribution is near-local, primarily from the New England shelf northeast of Nantucket. We disprove a previous hypothesis about Labrador Sea wind stress being an important driver of Nantucket sea-level variations. Buoyancy forcing, as important as wind stress in some years, includes local contributions as well as remote contributions from the subpolar North Atlantic that influence Nantucket sea level a few years later. Our rigorous adjoint-based analysis corroborates previous correlation-based studies indicating that sea-level variations in the subpolar gyre and along the United States northeast coast can both be influenced by subpolar buoyancy forcing. Forward perturbation experiments further indicate remote buoyancy forcing affects Nantucket sea level mostly through slow advective processes, although coastally trapped waves can cause rapid Nantucket sea level response within a few weeks.This research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). CGP was supported by NASA Sea Level Change Team awards 80NSSC20K1241 and 80NM0018D0004