Geothermal ocean warming discussion thread

by Judith Curry

“The atmosphere bias of climate science makes it impossible for them to see geological forces and therefore, impossible for them to understand the earth’s climate.” – Thongchai

When conducting the literature survey for my report on sea level rise [link; see section 4.2], I became intrigued by under-ocean heat sources.

Wunsch (2018) identified lower bounds on uncertainties in ocean temperature trends for the period 1994-2013. The trend in integrated ocean temperature was estimated by Wunsch to be 0.011 ± 0.001 oC/decade (note: this rate of warming is much less than the surface warming, owing to the large volume of ocean water). This corresponds to a 20- year average ocean heating rate of 0.48 ±0.1 W/m2 of which 0.1 W/m2 arises from the geothermal forcing. I have rarely seen geothermal forcing (e.g. underwater volcanoes) mentioned as a source of ocean warming – the numbers cited by Wunsch reflect nearly a 20% contribution by geothermal forcing to overall global ocean warming over the past two decades.”

Makes me wonder how much of the TOA radiative energy imbalance calculated from ocean heat content reflects seafloor geothermal heat fluxes?

Climate modelers are beginning to pay attention to seafloor geothermal fluxes.  The first such study that I’ve spotted is Adcroft et al. (2012), using a uniform geothermal heat flux of 50 W/m2 through the sea floor. They found substantial changes in deep circulation to this heat flux.

The GFDL ESM2 Global Coupled Climate-Carbon Earth System Model (2012) [link] states that it incorporates ocean geothermal heat flux following Adcroft et al.  I don’t know if this is what the current  (CMIP6) version of ESM2 uses.

The most interesting analysis that I’ve spotted on this is Downes et al. (2016) The transient response of Southern Ocean Circulation to Geothermal Heating in a Global Climate Model [link]

Abstract. Model and observational studies have concluded that geothermal heating significantly alters the global overturning circulation and the properties of the widely distributed Antarctic Bottom Water. Here two distinct geothermal heat flux datasets are tested under different experimental designs in a fully coupled model that mimics the control run of a typical Coupled Model Intercomparison Project (CMIP) climate model. The regional analysis herein reveals that bottom temperature and transport changes, due to the inclusion of geothermal heating, are propagated throughout the water column, most prominently in the Southern Ocean, with the background density structure and major circulation pathways acting as drivers of these changes. While geothermal heating enhances Southern Ocean abyssal overturning circulation by 20%–50%, upwelling of warmer deep waters and cooling of upper ocean waters within the Antarctic Circumpolar Current (ACC) region decrease its transport by 3–5 Sv (1 Sv = 106 m3 s−1). The transient responses in regional bottom temperature increases exceed 0.1°C. The large-scale features that are shown to transport anomalies far from their geothermal source all exist in the Southern Ocean. Such features include steeply sloping isopycnals, weak abyssal stratification, voluminous southward flowing deep waters and exported bottom waters, the ACC, and the polar gyres. Recently the Southern Ocean has been identified as a prime region for deep ocean warming; geothermal heating should be included in climate models to ensure accurate representation of these abyssal temperature changes.

This is by no means an exhaustive literature survey on incorporation of seafloor geothermal heat flux into ocean models, but I suspect that the GFDL model is the most advanced one in this regard.

The motivation for this particular thread is an email that I received today, and also some tweets I spotted.

The Miocene

Why the Miocene?  This blurb from the current AGU Call for Abstracts provides a good summary:

The Miocene (23 to 5.3 mya) is a crucial, dynamical interval in Earth’s history that provides unparalleled insights into the functioning of greenhouse climates.  At times during the Miocene, Antarctic ice volume was half modern, the Arctic Ocean was ice-free in winter, and extratropical temperatures nearly as warm as in the Eocene. This is an enigma, because the continental configurations and ocean circulation were much closer to modern than in the Paleogene, and atmospheric pCO2 was in the 300-600 ppm range.  Taken at face value, this implies either a system highly sensitive to greenhouse gas forcing or the presence of still unexplained forcings and feedbacks.

A series of papers on mid-ocean spreading zone seismic activity and global temperatures have been published by Arthur Viterito.

Modern climate

A series of papers on mid-ocean spreading zone seismic activity and global temperatures have been published by Arthur Viterito.

https://rclutz.wordpress.com/2016/10/05/overview-seafloor-eruptions-and-ocean-warming/

 

via Climate Etc.

https://ift.tt/2XUI3tJ

July 21, 2019 at 02:39PM

One Comment on “Geothermal ocean warming discussion thread

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