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  • AGU (American Geophysical Union)  (3)
  • Copernicus Publications (EGU)  (1)
  • 1
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    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 117 (C11). C11019.
    Publication Date: 2019-09-24
    Description: Observations indicate increasingly large and strong oxygen minimum zones (OMZs) in the tropical Pacific over recent decades. Here we report on oxygen decreases and variability within the eastern equatorial Pacific OMZ. We construct time series from historical and profiling float oxygen data and analyze data from repeat hydrographic sections at 110°W and 85°50′W. Historical data are quite sparse for constructing oxygen time series, but floats with oxygen sensors prove to be good tools to fill measurement gaps in later parts of these time series. In the region just south of the equator a time series over the last 34 years reveals that oxygen decreases from 200 to 700 m at a rate between 0.50 and 0.83 μmol kg−1 yr−1. This strong decrease seems to be related to changes in the Pacific Decadal Oscillation (PDO). Oscillations on shorter time scales (e.g., an El Niño signal in the upper 350 m) are superimposed upon this trend. In the section data, a general trend of decreasing oxygen is present below the surface layer. While velocity differences appear related to oxygen differences in the equatorial channel, there is less correlation elsewhere. Contrasting with long-term trend computations, the trends derived from two repeat sections are obscured by the influence of seasonal and longer-term variability. Multidecadal variability (e.g., PDO) has the strongest influence on long-term trends, while El Niño, isopycnal heave, current variability, seasonal cycles, and temperature changes are less important. Key points: - Oxygen decrease in the Pacific OMZ over the last 34 years in 200-700 m depth - Trends in oxygen and their relation to variability on different timescales - Relation between oxygen and velocity changes in the equatorial channel
    Type: Article , PeerReviewed
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  • 2
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    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 115 (C9). C09011.
    Publication Date: 2019-09-23
    Description: The supply of oxygen-rich water to the oxygen minimum zones (OMZs) of the eastern North and South Pacific via zonal tropical currents is investigated using shipboard acoustic Doppler current profiler and hydrographic section data. Near the equator, the Equatorial Undercurrent (EUC), Northern and Southern Subsurface Countercurrents (SCCs), and the Northern and Southern Intermediate Countercurrents (ICCs) all carry water that is oxygen richer than adjacent westward flows, thereby providing a net oxygen supply to the eastern Pacific OMZs. The synoptic velocity-weighted oxygen concentration difference between eastward and westward flows is typically 10–50 μmol kg−1. Subthermocline zonal oxygen fluxes reflect decreasing oxygen concentrations of the EUC, the SCCs, and the ICCs as they flow eastward. Approximately 30 year time series in well-sampled regions of the equatorial Pacific show oxygen content decreasing as rapidly as −0.55 μmol kg−1 yr−1 in the major oxygen supply paths of the OMZs for a 200–700 m layer and similar trends for a density layer spanning roughly these depths. This finding is in gross agreement with climate models, which generally predict expanding OMZs.
    Type: Article , PeerReviewed
    Format: text
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  • 3
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    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research - Oceans, 117 (C4). ..
    Publication Date: 2014-10-21
    Description: Temperature and salinity both contribute to ocean density, including its seasonal cycle and spatial patterns in the mixed layer. Temperature and salinity profiles from the Argo Program allow construction and analysis of a global, monthly, mixed layer climatology. Temperature changes dominate the seasonal cycle of mixed layer density in most regions, but salinity changes are dominant in the tropical warm pools, Arctic, and Antarctic. Under the Intertropical Convergence Zone, temperature and salinity work in concert to increase seasonal stratification, but the seasonal density changes there are weak because the temperature and salinity changes are small. In the eastern subtropics, seasonal salinity changes partly compensate those in temperature and reduce seasonal mixed layer density changes. Besides a hemispheric seasonal reversal, the times of maximum and minimum mixed layer density exhibit regional variations. For instance, the equatorial region is more closely aligned with Southern Hemisphere timing, and much of the North Indian Ocean has a minimum density in May and June. Outside of the tropics, the maximum mixed layer density occurs later in the winter toward the poles, and the minimum earlier in the summer. Finally, at the times of maximum mixed layer density, some of the ocean has horizontal temperature and salinity gradients that work against each other to reduce the horizontal density gradient. However, on the equatorial sides of the subtropical salinity maxima, temperature and salinity gradients reinforce each other, increasing the density gradients there. Density gradients are generally stronger where either salinity or temperature gradients are dominant influences.
    Type: Article , PeerReviewed
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  • 4
    Publication Date: 2024-02-07
    Description: The Earth climate system is out of energy balance, and heat has accumulated continuously over the past decades, warming the ocean, the land, the cryosphere, and the atmosphere. According to the Sixth Assessment Report by Working Group I of the Intergovernmental Panel on Climate Change, this planetary warming over multiple decades is human-driven and results in unprecedented and committed changes to the Earth system, with adverse impacts for ecosystems and human systems. The Earth heat inventory provides a measure of the Earth energy imbalance (EEI) and allows for quantifying how much heat has accumulated in the Earth system, as well as where the heat is stored. Here we show that the Earth system has continued to accumulate heat, with 381±61 ZJ accumulated from 1971 to 2020. This is equivalent to a heating rate (i.e., the EEI) of 0.48±0.1 W m−2. The majority, about 89 %, of this heat is stored in the ocean, followed by about 6 % on land, 1 % in the atmosphere, and about 4 % available for melting the cryosphere. Over the most recent period (2006–2020), the EEI amounts to 0.76±0.2 W m−2. The Earth energy imbalance is the most fundamental global climate indicator that the scientific community and the public can use as the measure of how well the world is doing in the task of bringing anthropogenic climate change under control. Moreover, this indicator is highly complementary to other established ones like global mean surface temperature as it represents a robust measure of the rate of climate change and its future commitment. We call for an implementation of the Earth energy imbalance into the Paris Agreement's Global Stocktake based on best available science. The Earth heat inventory in this study, updated from von Schuckmann et al. (2020), is underpinned by worldwide multidisciplinary collaboration and demonstrates the critical importance of concerted international efforts for climate change monitoring and community-based recommendations and we also call for urgently needed actions for enabling continuity, archiving, rescuing, and calibrating efforts to assure improved and long-term monitoring capacity of the global climate observing system. The data for the Earth heat inventory are publicly available, and more details are provided in Table 4.
    Type: Article , PeerReviewed
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