New paper finds sea levels were much higher than the present during almost all prior interglacials over past 5.3 million years – Published in Nature


By: - Climate DepotApril 18, 2014 12:50 PM

New paper finds sea levels were much higher than the present during almost all prior interglacials over past 5.3 million years

http://hockeyschtick.blogspot.com/2014/04/new-paper-finds-sea-levels-were-much.html

A paper published today in Nature reconstructs sea levels over the past 5.3 million years and shows that sea levels were higher than the present during almost every interglacial period over the past 5.3 million years. Sea levels at present during the current interglacial are indicated as the added red horizontal line at zero meters on Fig. 2 below, and excursions above this line indicate sea levels during past interglacials as much as 50+ meters [164+ feet] higher than present sea levels. Thus, there is no evidence that sea level rise during the present interglacial is unprecedented, unnatural, unusual or any different from that which occurred in prior interglacials, or any evidence of influence by man on sea levels. 

Fig. 2 with added red horizontal lines show present sea levels. Horizontal axis is thousands of years before the present. 

The last interglacial ~100,000 years ago [Eemian] had sea levels between 16-31 feet higher than the present, although it appears as a tiny blip above the red line in the graph a much more compressed scale above, but is better appreciated by this graph from another recent paper:

Sea levels during the last interglacial ~120,000 years ago were up to 5 meters higher than the present in this location and up to 9.5 meters higher at other locations

It is well known that interglacials have occurred at 100,000 year intervals over the past ~1 million years, and at intervals of ~44,000 years from ~1 million to 2.5 million years ago. 

The primary purpose of the paper is to help solve the mystery of what causes ice ages, yet appears to only deepen the mystery. Instead, the authors find a ~550,000 year gap between the onset of cooling and glaciation, whereas these were previously assumed to occur at the same time. 

The authors note, “We find that deep-sea temperature and sea level generally decreased through time, but distinctly out of synchrony, which is remarkable given the importance of ice-albedo feedbacks on the radiative forcing of climate,” thus implying that there are major problems with current global warming theory regarding ice-albedo positive feedbacks and radiative forcing. 

Crucial new information about how the ice ages came aboutDate: April 16, 2014Source: University of SouthamptonSummary: Scientists have discovered new relationships between deep-sea temperature and ice-volume changes to provide crucial new information about how the ice ages came about. The researchers found, for the first time, that the long-term trends in cooling and continental ice-volume cycles over the past 5.3 million years were not the same. In fact, for temperature the major step toward the ice ages that have characterized the past two to three million years was a cooling event at 2.7 million years ago, but for ice-volume the crucial step was the development of the first intense ice age at around 2.15 million years ago. Before these results, these were thought to have occurred together at about 2.5 million years ago.An international team of scientists has discovered new relationships between deep-sea temperature and ice-volume changes to provide crucial new information about how the ice ages came about.An international team of scientists has discovered new relationships between deep-sea temperature and ice-volume changes to provide crucial new information about how the ice ages came about.Researchers from the University of Southampton, the National Oceanography Centre and the Australian National University developed a new method for determining sea-level and deep-sea temperature variability over the past 5.3 million years. It provides new insight into the climatic relationships that caused the development of major ice-age cycles during the past two million years.The researchers found, for the first time, that the long-term trends in cooling and continental ice-volume cycles over the past 5.3 million years were not the same. In fact, for temperature the major step toward the ice ages that have characterised the past two to three million years was a cooling event at 2.7 million years ago, but for ice-volume the crucial step was the development of the first intense ice age at around 2.15 million years ago. Before these results, these were thought to have occurred together at about 2.5 million years ago.The results are published in the scientific journalNature.Co-author Dr Gavin Foster, from Ocean and Earth Science at the University of Southampton, says: “Our work focused on the discovery of new relationships within the natural Earth system. In that sense, the observed decoupling of temperature and ice-volume changes provides crucial new information for our understanding of how the ice ages developed.”However, there are wider implications too. For example, a more refined sea-level record over millions of years is commercially interesting because it allows a better understanding of coastal sediment sequences that are relevant to the petroleum industry. Our record is also of interest to climate policy developments, because it opens the door to detailed comparisons between past atmospheric CO2 concentrations, global temperatures, and sea levels, which has enormous value to long-term future climate projections.”The team used records of oxygen isotope ratios (which provide a record of ancient water temperature) from microscopic plankton fossils recovered from the Mediterranean Sea, spanning the last 5.3 million years. This is a particularly useful region because the oxygen isotopic composition of the seawater is largely determined by the flow of water through the Strait of Gibraltar, which in turn is sensitive to changes in global sea level — in a way like the pinching of a hosepipe.As continental ice sheets grew during the ice ages, flow through the Strait of Gibraltar was reduced, causing measurable increases in the oxygen isotope O-18 (8 protons and 10 neutrons) relative to O-16 (8 protons and 8 neutrons) in Mediterranean waters, which became preserved in the shells of the ancient plankton. Using long drill cores and uplifted sections of sea-floor sediments, previous work had analysed such microfossil-based oxygen isotope records from carefully dated sequences.The current study added a numerical model for calculating water exchange through the Strait of Gibraltar as a function of sea-level change, which allowed the microfossil records to be used as a sensitive recorder of global sea-level changes. The new sea-level record was then used in combination with existing deep-sea oxygen isotope records from the open ocean, to work out deep-sea temperature changes.Lead author, Professor Eelco Rohling of Australian National University, says: “This is the first step for reconstructions from the Mediterranean records. Our previous work has developed and refined this technique for Red Sea records, but in that location it is restricted to the last half a million years because there are no longer drill cores. In the Mediterranean, we could take it down all the way to 5.3 million years ago. There are uncertainties involved, so we included wide-ranging assessments of these, as well as pointers to the most promising avenues for improvement. This work lays the foundation for a concentrated effort toward refining and improving the new sea-level record.”Noting the importance of the Strait of Gibraltar to the analysis, co-author Dr Mark Tamisiea from the National Oceanography Centre, Southampton adds: “Flow through the Strait will depend not only on the ocean’s volume, but also on how the land in the region moves up and down in response to the changing water levels. We use a global model of changes in the ocean and the ice sheets to estimate the deformation and gravity changes in the region, and how that will affect our estimate of global sea-level change.”Story Source:The above story is based on materials provided by University of Southampton. Note: Materials may be edited for content and length.Journal Reference:E. J. Rohling, G. L. Foster, K. M. Grant, G. Marino, A. P. Roberts, M. E. Tamisiea, F. Williams. Sea-level and deep-sea-temperature variability over the past 5.3 million years. Nature, 2014; DOI: 10.1038/nature13230

Sea-level and deep-sea-temperature variability over the past 5.3 million years

E. J. Rohling,
G. L. Foster,
K. M. Grant,
G. Marino,
A. P. Roberts,
M. E. Tamisiea
& F. Williams

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Corresponding author

Nature (2014) doi:10.1038/nature13230

Received
 13 November 2013 
Accepted
 04 March 2014 
Published online
 16 April 2014

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Ice volume (and hence sea level) and deep-sea temperature are key measures of global climate change. Sea level has been documented using several independent methods over the past 0.5 million years (Myr). Older periods, however, lack such independent validation; all existing records are related to deep-sea oxygen isotope (δ18O) data that are influenced by processes unrelated to sea level. For deep-sea temperature, only one continuous high-resolution (Mg/Ca-based) record exists, with related sea-level estimates, spanning the past 1.5 Myr. Here we present a novel sea-level reconstruction, with associated estimates of deep-sea temperature, which independently validates the previous 0–1.5 Myr reconstruction and extends it back to 5.3 Myr ago. We find that deep-sea temperature and sea level generally decreased through time, but distinctly out of synchrony, which is remarkable given the importance of ice-albedo feedbacks on the radiative forcing of climate. In particular, we observe a large temporal offset during the onset of Plio-Pleistocene ice ages, between a marked cooling step at 2.73 Myr ago and the first major glaciation at 2.15 Myr ago. Last, we tentatively infer that ice sheets may have grown largest during glacials with more modest reductions in deep-sea temperature.

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