scholarly journals Secular change in atmospheric Ar∕N<sub>2</sub> and its implications for ocean heat uptake and Brewer–Dobson circulation

2021 ◽  
Vol 21 (2) ◽  
pp. 1357-1373
Author(s):  
Shigeyuki Ishidoya ◽  
Satoshi Sugawara ◽  
Yasunori Tohjima ◽  
Daisuke Goto ◽  
Kentaro Ishijima ◽  
...  
Keyword(s):  
Secular Trend ◽  
Heat Content ◽  
Secular Trends ◽  
Global Ocean ◽  
Secular Change ◽  
Seasonal Cycles ◽  
Interannual Variations ◽  
Ocean Heat Uptake ◽  
Increasing Trends ◽  
D Model

Abstract. Systematic measurements of the atmospheric Ar∕N2 ratio have been made at ground-based stations in Japan and Antarctica since 2012. Clear seasonal cycles of the Ar∕N2 ratio with summertime maxima were found at middle- to high-latitude stations, with seasonal amplitudes increasing with increasing latitude. Eight years of the observed Ar∕N2 ratio at Tsukuba (TKB) and Hateruma (HAT), Japan, showed interannual variations in phase with the observed variations in the global ocean heat content (OHC). We calculated secularly increasing trends of 0.75 ± 0.30 and 0.89 ± 0.60 per meg per year from the Ar∕N2 ratio observed at TKB and HAT, respectively, although these trend values are influenced by large interannual variations. In order to examine the possibility of the secular trend in the surface Ar∕N2 ratio being modified significantly by the gravitational separation in the stratosphere, two-dimensional model simulations were carried out by arbitrarily modifying the mass stream function in the model to simulate either a weakening or an enhancement of the Brewer–Dobson circulation (BDC). The secular trend of the Ar∕N2 ratio at TKB, corrected for gravitational separation under the assumption of weakening (enhancement) of BDC simulated by the 2-D model, was 0.60 ± 0.30 (0.88 ± 0.30) per meg per year. By using a conversion factor of 3.5 × 10−23 per meg per joule by assuming a one-box ocean with a temperature of 3.5 ∘C, average OHC increase rates of 17.1 ± 8.6 ZJ yr−1 and 25.1 ± 8.6 ZJ yr−1 for the period 2012–2019 were estimated from the corrected secular trends of the Ar∕N2 ratio for the weakened- and enhanced-BDC conditions, respectively. Both OHC increase rates from the uncorrected- and weakened-BDC secular trends of the Ar∕N2 ratio are consistent with 12.2 ± 1.2 ZJ yr−1 reported by ocean temperature measurements, while that from the enhanced-BDC is outside of the range of the uncertainties. Although the effect of the actual atmospheric circulation on the Ar∕N2 ratio is still unclear and longer-term observations are needed to reduce uncertainty of the secular trend of the surface Ar∕N2 ratio, the analytical results obtained in the present study imply that the surface Ar∕N2 ratio is an important tracer for detecting spatiotemporally integrated changes in OHC and BDC.

scholarly journals Secular change in atmospheric Ar/N<sub>2</sub> and its implications for ocean heat uptake and Brewer-Dobson circulation

2020 ◽  
Author(s):  
Shigeyuki Ishidoya ◽  
Satoshi Sugawara ◽  
Yasunori Tohjima ◽  
Daisuke Goto ◽  
Kentaro Ishijima ◽  
...  
Keyword(s):  
Conversion Factor ◽  
Secular Trend ◽  
Heat Content ◽  
Global Ocean ◽  
Secular Change ◽  
Seasonal Cycles ◽  
Dimensional Model ◽  
Ocean Heat Uptake ◽  
Increase Rate ◽  
Increasing Trends

Abstract. Systematic measurements of the atmospheric Ar/N2 ratio have been made at ground-based stations in Japan and Antarctica since 2012. Clear seasonal cycles of the Ar/N2 ratio with summertime maxima were found at middle to high latitude stations, with seasonal amplitudes increasing with increasing latitude. Eight years of the observed Ar/N2 ratio at Tsukuba and Hateruma, Japan showed not only secular increasing trends, but also interannual variations in phase with the observed variations in the global ocean heat content (OHC). The observed secular trend of the Ar/N2 ratio was 0.75±0.30 per meg yr-1. Sensitivity test by using a 2-dimensional model with the Brewer-Dobson circulation (BDC) scenarios indicated the possibility of the secular trend in the surface Ar/N2 ratio being modified significantly by the gravitational separation in the stratosphere. The secular trend of the Ar/N2 ratio, corrected for gravitational separation under the assumption of weakening of BDC simulated by the 2D model, was 0.60±0.30 per meg yr-1. By using a conversion factor of 3.5x10-23 per meg J-1 by assuming a 1-box ocean with a temperature of 3.5 °C, then an average OHC increase rate of 17.1±8.6 ZJ yr-1 for the period 2012–2019 was estimated from the corrected secular trend of the Ar/N2 ratio. This value is consistent with 12.2±1.2 ZJ yr-1 reported by ocean temperature measurements. The effect of the actual atmospheric circulation on the Ar/N2 ratio is still unclear, however the analytical results obtained in the present study imply that the surface Ar/N2 ratio is an important tracer for detecting spatiotemporally-integrated changes in OHC and BDC.

Estimating Global Ocean Heat Content Changes in the Upper 1800 m since 1950 and the Influence of Climatology Choice*

2014 ◽  
Vol 27 (5) ◽  
pp. 1945-1957 ◽  
Author(s):  
John M. Lyman ◽  
Gregory C. Johnson
Keyword(s):  
Heat Content ◽  
Ocean Heat Content ◽  
Global Ocean ◽  
Ocean Temperature ◽  
Vertical Separation ◽  
Ocean Heat Uptake ◽  
Expendable Bathythermograph ◽  
Heat Uptake ◽  
The Mean

Abstract Ocean heat content anomalies are analyzed from 1950 to 2011 in five distinct depth layers (0–100, 100–300, 300–700, 700–900, and 900–1800 m). These layers correspond to historic increases in common maximum sampling depths of ocean temperature measurements with time, as different instruments—mechanical bathythermograph (MBT), shallow expendable bathythermograph (XBT), deep XBT, early sometimes shallower Argo profiling floats, and recent Argo floats capable of worldwide sampling to 2000 m—have come into widespread use. This vertical separation of maps allows computation of annual ocean heat content anomalies and their sampling uncertainties back to 1950 while taking account of in situ sampling advances and changing sampling patterns. The 0–100-m layer is measured over 50% of the globe annually starting in 1956, the 100–300-m layer starting in 1967, the 300–700-m layer starting in 1983, and the deepest two layers considered here starting in 2003 and 2004, during the implementation of Argo. Furthermore, global ocean heat uptake estimates since 1950 depend strongly on assumptions made concerning changes in undersampled or unsampled ocean regions. If unsampled areas are assumed to have zero anomalies and are included in the global integrals, the choice of climatological reference from which anomalies are estimated can strongly influence the global integral values and their trend: the sparser the sampling and the bigger the mean difference between climatological and actual values, the larger the influence.

Historical ocean heat uptake in CMIP6 Earth System models: global and regional perspectives

2020 ◽  
Author(s):  
Till Kuhlbrodt ◽  
Aurore Voldoire ◽  
Matthew Palmer ◽  
Rachel Killick ◽  
Colin Jones
Keyword(s):  
Time Series ◽  
Climate Models ◽  
Global Climate ◽  
Heat Content ◽  
Global Ocean ◽  
Earth System ◽  
Ocean Heat Uptake ◽  
The Pacific ◽  
Heat Uptake ◽  
Earth System Models

&lt;p&gt;Ocean heat content is arguably one of the most relevant metrics for tracking global climate change and in particular the current global heating. Because of its enormous heat capacity, the global ocean stores about 93 percent of the excess heat in the Earth System. Time series of global ocean heat content (OHC) closely track Earth&amp;#8217;s energy imbalance as observed as the net radiative balance at the top of the atmosphere. For these reasons simulated OHC time series are a cornerstone for assessing the scientific performance of Earth System models (ESM) and global climate models. Here we present a detailed analysis of the OHC change in simulations of the historical climate (20&lt;sup&gt;th&lt;/sup&gt; century up to 2014) performed with four of the current, state-of-the art generation of ESMs and climate models. These four models are UKESM1, HadGEM3-GC3.1-LL, CNRM-ESM2-1 and CNRM-CM6-1. All four share the same ocean component, NEMO3.6 in the shaconemo eORCA1 configuration, and they all take part in CMIP6, the current Phase 6 of the Coupled Model Intercomparison Project. Analysing a small number of models gives us the opportunity to analyse OHC change for the global ocean as well as for individual ocean basins. In addition to the ensemble means, we focus on some individual ensemble members for a more detailed process understanding. For the global ocean, the two CNRM models reproduce the observed OHC change since the 1960s closely, especially in the top 700 m of the ocean. The two UK models (UKESM1 and HadGEM3-GC3.1-LL) do not simulate the observed global ocean warming in the 1970s and 1980s, and they warm too fast after 1991. We analyse how this varied performance across the models relates to the simulated radiative forcing of the atmosphere. All four models show a smaller ocean heat uptake since 1971, and a larger transient climate response (TCR), than the CMIP5 ensemble mean. Close analysis of a few individual ensemble members indicates a dominant role of heat uptake and deep-water formation processes in the Southern Ocean for variability and change in global OHC. Evaluating OHC change in individual ocean basins reveals that the lack of warming in the UK models stems from the Pacific and Indian basins, while in the Atlantic the OHC change 1971-2014 is close to the observed value. Resolving the ocean warming in depth and time shows that regional ocean heat uptake in the North Atlantic plays a substantial role in compensating small warming rates elsewhere. An opposite picture emerges from the CNRM models. Here the simulated OHC change is close to observations in the Pacific and Indian basins, while tending to be too small in the Atlantic, indicating a markedly different role for the Atlantic meridional overturning circulation (AMOC) and cross-equatorial heat transport in these models.&lt;/p&gt;

Temporal variability of inferred surface energy fluxes derived from the ERA5 energy budget

2020 ◽  
Author(s):  
Johannes Mayer ◽  
Michael Mayer ◽  
Leopold Haimberger
Keyword(s):  
Surface Energy ◽  
Energy Budget ◽  
Temporal Variability ◽  
Heat Content ◽  
Global Ocean ◽  
High Temporal Resolution ◽  
Energy Fluxes ◽  
Ocean Heat Uptake ◽  
Surface Energy Fluxes ◽  
Global Mean

&lt;p&gt;We use the new Copernicus ERA5 reanalysis dataset to evaluate the global atmospheric energy budget using a consistent diagnostic framework and &amp;#160;improved numerical methods. A main outcome of this work are mass consistent divergences of moist static plus kinetic energy fluxes. These divergences are combined with top-of-the-atmosphere fluxes based on satellite observations and reconstructions back to 1985 to obtain net surface energy fluxes (F&lt;sub&gt;S&lt;/sub&gt;) with unprecedented accuracy. The global mean of these F&lt;sub&gt;S&lt;/sub&gt; fields is unbiased by construction. Hence, this product is well-suited for climate studies and model evaluations. &amp;#160;Here, the temporal variability and stability of inferred F&lt;sub&gt;S&lt;/sub&gt;, the land-ocean energy transport and the corresponding water cycle are presented and compared with previous evaluations, which used ERA-Interim.&amp;#160;&lt;/p&gt;&lt;p&gt;The inferred F&lt;sub&gt;S&lt;/sub&gt; fields exhibit a much smaller noise level, and sampling errors are drastically reduced due to the high temporal resolution (hourly) of the ERA5 dataset. Energy budget residuals over land are on the order of 17.0 Wm&lt;sup&gt;-2&lt;/sup&gt;, which represents a 63 % reduction compared to ERA-Interim. We also present time series of F&lt;sub&gt;S&lt;/sub&gt; averaged over the global ocean. Its global mean is 2.0 Wm&lt;sup&gt;-2&lt;/sup&gt;, which is in much better agreement with ocean heat uptake than widely used satellite-derived surface flux products. Moreover, it exhibits reasonable temporal stability at least from 2000 onwards. We compare the annual cycles of F&lt;sub&gt;S&lt;/sub&gt; over the ocean and ocean heat content variations derived from ocean reanalysis products and find good agreement. Overall, our results demonstrate clear improvements over earlier evaluations, but more work is needed to optimally use the available data and further reduce uncertainties.&lt;/p&gt;

Recent trajectory of ocean heat uptake estimated from novel 1972-2017 ocean sea-ice model hindcast simulations

2021 ◽  
Author(s):  
Maurice Huguenin ◽  
Ryan Holmes ◽  
Matthew England
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Heat Content ◽  
Anthropogenic Heat ◽  
Global Ocean ◽  
Ocean Heat Uptake ◽  
Heat Uptake ◽  
The Tropics ◽  
And Storage ◽  
Ice Model

&lt;p&gt;Uptake and storage of heat by the ocean plays a critical role in modulating the Earth's climate system. In the last 50 years, the ocean has absorbed over 90% of the additional energy accumulating in the Earth system due to radiative imbalance. However, our knowledge about ocean heat uptake (OHU), transport and storage is strongly constrained by the sparse observational record with large uncertainties. In this study, we conduct a suite of historical 1972&amp;#8211;2017 hindcast simulations using a global ocean-sea ice model that are specifically designed to account for a cold start climate and model drift. The hindcast simulations are initialised from an equilibrated control simulation that uses repeat decade forcing over the period 1962-1971. This repeat decade forcing approach is a compromise between an early unobserved period (where our confidence in the forcing is low) and later periods (which would result in a shorter experiment period and a smaller fraction of the total OHU). The simulations are aimed at giving a good estimate of the trajectory of OHU in the tropics, the extratropics and individual ocean basins in recent decades. Many modelling studies that look at recent OHU rates so far use a simpler approach for the forcing. For example, they use repeating cycles of 1950-2010 Coordinated Ocean Reference Experiment (CORE) forcing that is consistent with the Ocean Model Intercomparison Project 2 (OMIP-2). However, this approach cannot account for model drift. The new simulations here highlight the dominant role of the extratropics, and in particular the Southern Ocean in OHU. In contrast, little heat is absorbed in the tropics and simulations forced with only tropical trends in atmospheric forcing show only weak global ocean heat content trends. Almost 50% of the heat taken up from the atmosphere in the Southern Ocean is transported into the Atlantic Ocean. Two-thirds of this Southern Ocean-sourced heat is then subsequently lost to the atmosphere in the North Atlantic but nevertheless this basin gains heat overall. Our results help to estimate the large-scale cycling of anthropogenic heat within the ocean today and have implications for heat content trends under a changing climate.&lt;/p&gt;

scholarly journals Global representation of tropical cyclone-induced ocean thermal changes using Argo data – Part 2: Estimating air–sea heat fluxes and ocean heat content changes

2014 ◽  
Vol 11 (6) ◽  
pp. 2907-2937
Author(s):  
L. Cheng ◽  
J. Zhu ◽  
R. L. Sriver
Keyword(s):  
Heat Loss ◽  
Heat Budget ◽  
Heat Content ◽  
Global Scale ◽  
Heat Fluxes ◽  
Ocean Heat Content ◽  
Global Ocean ◽  
Storm Events ◽  
Argo Data ◽  
Ocean Heat Uptake

Abstract. We use Argo temperature data to examine changes in ocean heat content (OHC) and air–sea heat fluxes induced by tropical cyclones (TC)s on a global scale. A footprint technique that analyzes the vertical structure of cross-track thermal responses along all storm tracks during the period 2004–2012 is utilized (see part I). We find that TCs are responsible for 1.87 PW (11.05 W m−2 when averaging over the global ocean basin) of heat transfer annually from the global ocean to the atmosphere during storm passage (0–3 days) on a global scale. Of this total, 1.05 ± 0.20 PW (4.80 ± 0.85 W m−2) is caused by Tropical storms/Tropical depressions (TS/TD) and 0.82 ± 0.21 PW (6.25 ± 1.5 W m−2) is caused by hurricanes. Our findings indicate that ocean heat loss by TCs may be a substantial missing piece of the global ocean heat budget. Net changes in OHC after storm passage is estimated by analyzing the temperature anomalies during wake recovery following storm events (4–20 days after storm passage) relative to pre-storm conditions. Results indicate the global ocean experiences a 0.75 ± 0.25 PW (5.98 ± 2.1W m−2) net heat gain annually for hurricanes. In contrast, under TS/TD conditions, ocean experiences 0.41 ± 0.21 PW (1.90 ± 0.96 W m−2) net ocean heat loss, suggesting the overall oceanic thermal response is particularly sensitive to the intensity of the event. The net ocean heat uptake caused by all storms is 0.34 PW.

scholarly journals Ocean Heat Uptake and Interbasin Transport of the Passive and Redistributive Components of Surface Heating

2016 ◽  
Vol 29 (20) ◽  
pp. 7507-7527 ◽  
Author(s):  
Oluwayemi A. Garuba ◽  
Barry A. Klinger
Keyword(s):  
Heat Flux ◽  
Heat Input ◽  
Surface Heat Flux ◽  
Heat Content ◽  
Surface Heat ◽  
Global Ocean ◽  
Passive Component ◽  
Ocean Heat Uptake ◽  
Anomalous Surface ◽  
Heat Uptake

Abstract Global warming induces ocean circulation changes that not only can redistribute ocean reservoir temperature stratification but also change the total heat content anomaly of the ocean. Here all consequences of this process are referred to collectively as “redistribution.” Previous model studies of redistributive effects could not measure the net global contribution to the amount of ocean heat uptake by redistribution. In this study, a global ocean model experiment with abrupt increase in surface temperature is conducted with a new passive tracer formulation. This separates ocean heat uptake into contributions due to redistribution temperature and surface heat flux anomalies and those due to the passive advection and mixing of surface heat flux anomalies forced in the atmosphere. For a decline in the Atlantic meridional overturning circulation of about 40%, redistribution nearly doubles the Atlantic passive anomalous surface heat input and depth penetration of temperature anomalies. However, smaller increases in the Indian and Pacific Oceans cause the net global redistributive contribution to be only 25% of the passive contribution. Despite the much larger anomalous surface heat input in the Atlantic, the Pacific gains heat content anomaly similar to that in the Atlantic because of export from the Atlantic and Indian Oceans via the global conveyor belt. Of this interbasin heat transport, most of the passive component comes from the Indian Ocean and the redistributive component comes from the Atlantic.

scholarly journals Decadal Ocean Heat Redistribution Since the Late 1990s and Its Association with Key Climate Modes

Climate ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 91 ◽  
Author(s):  
Lijing Cheng ◽  
Gongjie Wang ◽  
John Abraham ◽  
Gang Huang
Keyword(s):  
Climate Models ◽  
Southern Oscillation ◽  
Three Dimensional ◽  
Heat Content ◽  
Single Mode ◽  
Global Ocean ◽  
Ocean Heat Uptake ◽  
Climate Modes ◽  
Surface Warming ◽  
Decadal Scale

Ocean heat content (OHC) is the major component of the earth’s energy imbalance. Its decadal scale variability has been heavily debated in the research interest of the so-called “surface warming slowdown” (SWS) that occurred during the 1998–2013 period. Here, we first clarify that OHC has accelerated since the late 1990s. This finding refutes the concept of a slowdown of the human-induced global warming. This study also addresses the question of how heat is redistributed within the global ocean and provides some explanation of the underlying physical phenomena. Previous efforts to answer this question end with contradictory conclusions; we show that the systematic errors in some OHC datasets are partly responsible for these contradictions. Using an improved OHC product, the three-dimensional OHC changes during the SWS period are depicted, related to a reference period of 1982–1997. Several “hot spots” and “cold spots” are identified, showing a significant decadal-scale redistribution of ocean heat, which is distinct from the long-term ocean-warming pattern. To provide clues for the potential drivers of the OHC changes during the SWS period, we examine the OHC changes related to the key climate modes by regressing the Pacific Decadal Oscillation (PDO), El Niño-Southern Oscillation (ENSO), and Atlantic Multi-decadal Oscillation (AMO) indices onto the de-trended gridded OHC anomalies. We find that no single mode can fully explain the OHC change patterns during the SWS period, suggesting that there is not a single “pacemaker” for the recent SWS. Our observation-based analyses provide a basis for further understanding the mechanisms of the decadal ocean heat uptake and evaluating the climate models.

Pathways and time scales of ocean heat uptake and redistribution in a global ocean-ice model

2020 ◽  
Author(s):  
Alice Marzocchi ◽  
George Nurser ◽  
Louis Clement ◽  
Elaine McDonagh
Keyword(s):  
Time Scales ◽  
Ocean Circulation ◽  
Mass Production ◽  
Water Mass ◽  
Heat Content ◽  
Global Ocean ◽  
Relative Role ◽  
Passive Tracer ◽  
Ocean Heat Uptake ◽  
Ice Model

&lt;p&gt;Changes in regional ocean heat content are not only sensitive to anthropogenic and natural influences, but also substantially impacted by the redistribution of heat, which is in turn driven by changes in ocean circulation and air-sea fluxes. Using a set of numerical simulations with an ocean-sea-ice model of the NEMO framework, we assess where the ocean takes up heat from the atmosphere and how ocean currents transport and redistribute that heat. Here, the strength and patterns of the net uptake of heat by the ocean are treated like a passive tracer, by including simulated sea water vintage dyes, which are released annually between 1958 and 2017. An additional tracer released in year 1800 is also used to investigate longer-term variability. All dye tracers are released from 29 surface patches, representing different water mass production sites, allowing us to identify when and where water masses were last ventilated. The tracers&amp;#8217; distribution and fluxes are shown to capture years of strong and weak convection at deep and mode water formation sites in both hemispheres, when compared to the available observations. Using this approach, which can be applied to any passive tracer in the ocean, we can: (1) assess the relative role of each of the water mass production sites, (2) evaluate the regional and depth distribution of the tracers, and (3) determine their variability on interannual, multidecadal and centennial time scales.&lt;/p&gt;

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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