scholarly journals World Ocean Thermocline Weakening and Isothermal Layer Warming

2020 ◽  
Vol 10 (22) ◽  
pp. 8185
Author(s):  
Peter C. Chu ◽  
Chenwu Fan
Keyword(s):  
World Ocean ◽  
Heat Content ◽  
Global Ocean ◽  
Upper Ocean ◽  
Polar Regions ◽  
Depth Range ◽  
Isothermal Layer ◽  
Warming Rate ◽  
Open Datasets ◽  
Depth Ranges

This paper identifies world thermocline weakening and provides an improved estimate of upper ocean warming through replacement of the upper layer with the fixed depth range by the isothermal layer, because the upper ocean isothermal layer (as a whole) exchanges heat with the atmosphere and the deep layer. Thermocline gradient, heat flux across the air–ocean interface, and horizontal heat advection determine the heat stored in the isothermal layer. Among the three processes, the effect of the thermocline gradient clearly shows up when we use the isothermal layer heat content, but it is otherwise when we use the heat content with the fixed depth ranges such as 0–300 m, 0–400 m, 0–700 m, 0–750 m, and 0–2000 m. A strong thermocline gradient exhibits the downward heat transfer from the isothermal layer (non-polar regions), makes the isothermal layer thin, and causes less heat to be stored in it. On the other hand, a weak thermocline gradient makes the isothermal layer thick, and causes more heat to be stored in it. In addition, the uncertainty in estimating upper ocean heat content and warming trends using uncertain fixed depth ranges (0–300 m, 0–400 m, 0–700 m, 0–750 m, or 0–2000 m) will be eliminated by using the isothermal layer. The isothermal layer heat content with the monthly climatology removed (i.e., relative isothermal layer heat content) is calculated for an individual observed temperature profile from three open datasets. The calculated 1,111,647 pairs of (thermocline gradient, relative isothermal layer heat content) worldwide show long-term decreasing of the thermocline gradient and increasing of isothermal layer heat content in the global as well as regional oceans. The global ocean thermocline weakening rate is (−2.11 ± 0.31) × 10−3 (°C m−1 yr−1) and isothermal layer warming rate is (0.142 ± 0.014) (W m−2).

scholarly journals Is the Upper Ocean Warming? Comparisons of 50-Year Trends from Different Analyses*

2008 ◽  
Vol 21 (10) ◽  
pp. 2259-2268 ◽  
Author(s):  
Mark Carson ◽  
D. E. Harrison
Keyword(s):  
World Ocean ◽  
Heat Content ◽  
Global Ocean ◽  
Upper Ocean ◽  
Ocean Temperature ◽  
Regional Trend ◽  
Upper Ocean Heat Content ◽  
Temperature Trends ◽  
Temporal And Spatial ◽  
Estimate Uncertainty

Abstract There is great interest in World Ocean temperature trends, yet the historical global ocean database has very uneven coverage in space and time. Previous work on 50-yr upper ocean temperature trends from the NOAA ocean data archive is extended here. Trends at depths from 50 to 1000 m are examined, based on observations gridded over larger regions than in the earlier study. Despite the use of larger grid boxes, most of the ocean does not have significant 50-yr trends at the 90% confidence level (CL). In fact only 30% of the ocean at 50 m has 90% CL trends, and the percentage decreases significantly with increasing depth. As noted in the previous study, there is much spatial structure in 50-yr trends, with areas of strong warming and strong cooling. These trend results are compared with trends calculated from data interpolated to standard levels and from a highly horizontally interpolated version of the dataset that has been used in previous heat content trend studies. The regional trend results can differ substantially, even in the areas with statistically significant trends. Trends based on the more interpolated analyses show more warming. Together with major temporal and spatial sampling limitations, the previously described strong interdecadal and spatial variability of trends makes it very difficult to formally estimate uncertainty in World Ocean averages, but these results suggest that upper ocean heat content integrals and integral trends may be substantially more uncertain than has yet been acknowledged. Further exploration of uncertainties is needed.

scholarly journals Multidecadal Warming and Density Loss in the Deep Weddell Sea, Antarctica

2020 ◽  
Vol 33 (22) ◽  
pp. 9863-9881
Author(s):  
Volker H. Strass ◽  
Gerd Rohardt ◽  
Torsten Kanzow ◽  
Mario Hoppema ◽  
Olaf Boebel
Keyword(s):  
Radiative Forcing ◽  
World Ocean ◽  
Accurate Method ◽  
Weddell Sea ◽  
Global Ocean ◽  
Polar Regions ◽  
Weddell Gyre ◽  
Temperature Trends ◽  
Northern Edge ◽  
Circumpolar Current

AbstractThe World Ocean is estimated to store more than 90% of the excess energy resulting from man-made greenhouse gas–driven radiative forcing as heat. Uncertainties of this estimate are related to undersampling of the subpolar and polar regions and of the depths below 2000 m. Here we present measurements from the Weddell Sea that cover the whole water column down to the sea floor, taken by the same accurate method at locations revisited every few years since 1989. Our results show widespread warming with similar long-term temperature trends below 700-m depth at all sampling sites. The mean heating rate below 2000 m exceeds that of the global ocean by a factor of about 5. Salinity tends to increase—in contrast to other Southern Ocean regions—at most sites and depths below 700 m, but nowhere strongly enough to fully compensate for the warming effect on seawater density, which hence shows a general decrease. In the top 700 m neither temperature nor salinity shows clear trends. A closer look at the vertical distribution of changes along an approximately zonal and a meridional section across the Weddell Gyre reveals that the strongest vertically coherent warming is observed at the flanks of the gyre over the deep continental slopes and at its northern edge where the gyre connects to the Antarctic Circumpolar Current (ACC). Most likely, the warming of the interior Weddell Sea is driven by changes of the Weddell Gyre strength and its interaction with the ACC.

scholarly journals In Situ–Based Reanalysis of the Global Ocean Temperature and Salinity with ISAS: Variability of the Heat Content and Steric Height

2016 ◽  
Vol 29 (4) ◽  
pp. 1305-1323 ◽  
Author(s):  
Fabienne Gaillard ◽  
Thierry Reynaud ◽  
Virginie Thierry ◽  
Nicolas Kolodziejczyk ◽  
Karina von Schuckmann
Keyword(s):  
Southern Ocean ◽  
World Ocean ◽  
Heat Content ◽  
Absolute Error ◽  
Ocean Heat Content ◽  
Global Ocean ◽  
Analysis Tool ◽  
Steric Height ◽  
The Impact

Abstract The In Situ Analysis System (ISAS) was developed to produce gridded fields of temperature and salinity that preserve as much as possible the time and space sampling capabilities of the Argo network of profiling floats. Since the first global reanalysis performed in 2009, the system has evolved, and a careful delayed-mode processing of the 2002–12 dataset has been carried out using version 6 of ISAS and updating the statistics to produce the ISAS13 analysis. This last version is now implemented as the operational analysis tool at the Coriolis data center. The robustness of the results with respect to the system evolution is explored through global quantities of climatological interest: the ocean heat content and the steric height. Estimates of errors consistent with the methodology are computed. This study shows that building reliable statistics on the fields is fundamental to improve the monthly estimates and to determine the absolute error bars. The new mean fields and variances deduced from the ISAS13 reanalysis and dataset show significant changes relative to the previous ISAS estimates, in particular in the Southern Ocean, justifying the iterative procedure. During the decade covered by Argo, the intermediate waters appear warmer and saltier in the North Atlantic and fresher in the Southern Ocean than in World Ocean Atlas 2005 long-term mean. At interannual scale, the impact of ENSO on the ocean heat content and steric height is observed during the 2006/07 and 2009/10 events captured by the network.

Forced and chaotic variability of basin-scale heat budgets in the global ocean: focus on the South Atlantic crossroads.

2020 ◽  
Author(s):  
Thierry Penduff ◽  
Fei-Er Yan ◽  
Imane Benabicha ◽  
Jean-Marc Molines ◽  
Bernard Barnier
Keyword(s):  
Southern Ocean ◽  
Heat Transport ◽  
Large Scale ◽  
World Ocean ◽  
Low Frequency ◽  
Heat Content ◽  
Global Ocean ◽  
Substantial Contribution ◽  
Atlantic Sector ◽  
Basin Scale

<p>The OCCIPUT eddy-permitting (1/4°) global ocean/sea-ice 50-member ensemble simulation is analyzed over the period 1980-2015 to identify how the atmosphere and the intrinsic/chaotic ocean variability modulate the basin-scale Ocean Heat Content (OHC) at various timescales. In all regions of the simulated world ocean, the atmospherically-forced interannual OHC variability is driven by both air-sea heat fluxes (Qnet) and advective heat transport convergences (Conv), while the intrinsic component is driven by Conv, and damped by Qnet. </p><p>We focus on the Atlantic sector of the Southern Ocean (SA), where the oceanic “chaos” explains 36 to 90% of the interannual and decadal heat transport variability across the limits of the basin, and 22% of this huge basin’s OHC variability at interannual and decadal timescales.</p><p>The model also simulates the Antarctic Circumpolar Wave (ACW) that was observed in the 80-90’s, with large impacts on OHC and heat transports in the Southern Ocean. This forced signal appears south of Australia, propagates eastward around Antarctica and northward into the Tropical Atlantic and the Tropical Indian Ocean. </p><p>These results highlight the substantial contribution of large-scale low-frequency chaotic heat advection in eddy-active regions, and its major impact on decadal OHC variations over key basins. They suggest that climate simulations using eddying ocean models include an oceanic and random source of large-scale low-frequency variability whose atmospheric impacts remain to be assessed.</p>

scholarly journals Time, Probe Type, and Temperature Variable Bias Corrections to Historical Expendable Bathythermograph Observations

2014 ◽  
Vol 31 (8) ◽  
pp. 1793-1825 ◽  
Author(s):  
Lijing Cheng ◽  
Jiang Zhu ◽  
Rebecca Cowley ◽  
Tim Boyer ◽  
Susan Wijffels
Keyword(s):  
Water Temperature ◽  
World Ocean ◽  
Heat Content ◽  
Terminal Velocity ◽  
Global Scale ◽  
Global Ocean ◽  
Probe Type ◽  
Fall Rate ◽  
Dominant Term ◽  
Expendable Bathythermograph

Abstract Systematic biases in historical expendable bathythermograph (XBT) data are examined using two datasets: 4151 XBT–CTD side-by-side pairs from 1967 to 2011 and 218 653 global-scale XBT–CTD pairs (within one month and 1°) extracted from the World Ocean Database 2009 (WOD09) from 1966 to 2010. Using the side-by-side dataset, it was found that both the pure thermal bias and the XBT fall rate (from which the depth of observation is calculated) increase with water temperature. Correlations between the terminal velocity A and deceleration B terms of the fall-rate equation (FRE) and between A and the offset from the surface terms are obtained, with A as the dominant term in XBT fall-rate behavior. To quantify the time variation of the XBT fall-rate and pure temperature biases, global-scale XBT–CTD pairs are used. Based on the results from the two datasets, a new correction scheme for historical XBT data is proposed for nine independent probe-type groups. The scheme includes corrections for both temperature and depth records, which are all variable with calendar year, water temperature, and probe type. The results confirm those found in previous studies: a slowing in fall rate during the 1970s and 2000s and the large pure thermal biases during 1970–85. The performance of nine different correction schemes is compared. After the proposed corrections are applied to the XBT data in the WOD09 dataset, global ocean heat content from 1967 to 2010 is reestimated.

scholarly journals Remote subsurface ocean temperature as a predictor of Atlantic hurricane activity

2018 ◽  
Vol 115 (45) ◽  
pp. 11460-11464 ◽  
Author(s):  
Enrico Scoccimarro ◽  
Alessio Bellucci ◽  
Andrea Storto ◽  
Silvio Gualdi ◽  
Simona Masina ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
Wind Shear ◽  
Heat Content ◽  
Global Ocean ◽  
Trade Wind ◽  
Upper Ocean ◽  
Ocean Temperature ◽  
Atlantic Hurricane ◽  
Hurricane Activity

Predicting North Atlantic hurricane activity months in advance is of great potential societal significance. The ocean temperature, both in terms of North Atlantic/tropical averages and upper ocean heat content, is demonstrated to be a significant predictor. To investigate the relationship between the thermal state of the Atlantic Ocean and the tropical cyclone (TC) activity in terms of accumulated cyclone energy (ACE), we use observed 1980–2015 TC records and a 1/4° resolution global ocean reanalysis. This paper highlights the nonlocal effect associated with eastern Atlantic Ocean temperature, via a reduction of wind shear, and provides additional predictive skill of TC activity, when considering subsurface temperature instead of sea surface temperature (SST) only. The most active TC seasons occur for lower than normal wind shear conditions over the main development region, which is also driven by reduced trade wind strength. A significant step toward operationally reliable TC activity predictions is gained after including upper ocean mean temperatures over the eastern Atlantic domain. Remote effects are found to provide potential skill of ACE up to 3 months in advance. These results indicate that consideration of the upper 40-m ocean average temperature improves upon a prediction of September Atlantic hurricane activity using only SST.

Warming of the Global Ocean: Spatial Structure and Water-Mass Trends

2016 ◽  
Vol 29 (13) ◽  
pp. 4949-4963 ◽  
Author(s):  
Sirpa Häkkinen ◽  
Peter B. Rhines ◽  
Denise L. Worthen
Keyword(s):  
Southern Hemisphere ◽  
Time Scales ◽  
World Ocean ◽  
Heat Content ◽  
Global Ocean ◽  
Water Volume ◽  
North Atlantic Current ◽  
Mode Water ◽  
Surface Warming ◽  
Recirculation Gyre

Abstract This study investigates the multidecadal warming and interannual-to-decadal heat content changes in the upper ocean (0–700 m), focusing on vertical and horizontal patterns of variability. These results support a nearly monotonic warming over much of the World Ocean, with a shift toward Southern Hemisphere warming during the well-observed past decade. This is based on objectively analyzed gridded observational datasets and on a modeled state estimate. Besides the surface warming, a warming climate also has a subsurface effect manifesting as a strong deepening of the midthermocline isopycnals, which can be diagnosed directly from hydrographic data. This deepening appears to be a result of heat entering via subduction and spreading laterally from the high-latitude ventilation regions of subtropical mode waters. The basin-average multidecadal warming mainly expands the subtropical mode water volume, with weak changes in the temperature–salinity (θ–S) relationship (known as “spice” variability). However, the spice contribution to the heat content can be locally large, for example in Southern Hemisphere. Multidecadal isopycnal sinking has been strongest over the southern basins and weaker elsewhere with the exception of the Gulf Stream/North Atlantic Current/subtropical recirculation gyre. At interannual to decadal time scales, wind-driven sinking and shoaling of density surfaces still dominate ocean heat content changes, while the contribution from temperature changes along density surfaces tends to decrease as time scales shorten.

scholarly journals 20th century cooling of the deep ocean contributed to delayed acceleration of Earth’s energy imbalance

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
A. Bagnell ◽  
T. DeVries
Keyword(s):  
20Th Century ◽  
Heat Content ◽  
Deep Ocean ◽  
Ocean Warming ◽  
Ocean Heat Content ◽  
Global Ocean ◽  
Energy Imbalance ◽  
Delayed Onset ◽  
The Past ◽  
Historical Reconstructions

AbstractThe historical evolution of Earth’s energy imbalance can be quantified by changes in the global ocean heat content. However, historical reconstructions of ocean heat content often neglect a large volume of the deep ocean, due to sparse observations of ocean temperatures below 2000 m. Here, we provide a global reconstruction of historical changes in full-depth ocean heat content based on interpolated subsurface temperature data using an autoregressive artificial neural network, providing estimates of total ocean warming for the period 1946-2019. We find that cooling of the deep ocean and a small heat gain in the upper ocean led to no robust trend in global ocean heat content from 1960-1990, implying a roughly balanced Earth energy budget within −0.16 to 0.06 W m−2 over most of the latter half of the 20th century. However, the past three decades have seen a rapid acceleration in ocean warming, with the entire ocean warming from top to bottom at a rate of 0.63 ± 0.13 W m−2. These results suggest a delayed onset of a positive Earth energy imbalance relative to previous estimates, although large uncertainties remain.

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