New paper finds sea levels rising at less than 4 inches per century, with no acceleration

A new paper finds global mean sea levels rose at only 1 mm/year, equivalent to less than 4 inches per century, over the 203 year period from 1807-2010. The finding is remarkably similar to the sea level rise of 1.1-1.3 mm/yr found by the NOAA 2005-2012 Sea Level Budget, the only sea level budget which reconciles both satellite [altimeters & GRACE] & ARGO float data. The authors also find no evidence of acceleration of sea level rise, which indicates that there is no evidence of a human influence upon sea levels. In addition, the authors find that sea level rise is a localized rather than global phenomenon, with 61% of tide gauge records demonstrating no change in sea levels, 4% showing a decrease, and a minority of 35% showing a rise. This implies relative sea level change is primarily related to subsidence or post-glacial rebound [land height changes] rather than melting ice or steric sea level changes [thermal expansion from warming]. 

Excerpts:

If SLR is accelerating, sea levels should be nonstationary in first differences, but stationary in second differences. In none of the tide gauges and segments do the Dickey-Fuller and KPSS statistics support the accelerationist hypothesis. [i.e. there was no acceleration] 

The substantive contribution of the paper is concerned with recent SLR in different parts of the world. Consensus estimates of recent GMSL rise are about 2mm/year. Our estimate is 1 mm/year. We suggest that the difference between the two estimates is induced by the widespread use of data reconstructions which inform the consensus estimates. There are two types of reconstruction. The first refers to reconstructed data for tide gauges in PSMSL prior to their year of installation. The second refers to locations where there are no tide gauges at all. Since the tide gauges currently in PSMSL are a quasi-random sample, our estimate of current GMSL rise is unbiased. If this is true, reconstruction bias is approximately 1mm/year.  

Sea level rise is regional rather than global and is concentrated in the southern Baltic, the Ring of Fire, and the Atlantic coast of the US. By contrast the north-west Pacific coast and north-east coast of India are characterized by sea level fall. In the minority of locations where sea levels are rising the mean increase is about 4 mm/year and in some locations it is as large as 9 mm/year. The fact that sea level rise is not global should not detract from its importance in those parts of the world where it is a serious problem.

Sea level rise is regional rather than global and is concentrated in the southern Baltic, the Ring of Fire, and the Atlantic coast of the US. By contrast the north-west Pacific coast and north-east coast of India are characterized by sea level fall.

TIDE GAUGE LOCATION AND THE MEASUREMENT OF GLOBAL SEA LEVEL RISE

Michael Beenstock 1 Daniel Felsenstein 2, Eyal Frank1, Yaniv Reingewertz 1

1 Department of Economics, Hebrew University of Jerusalem, Jerusalem 91905, 
Israel
2 Department of Geography, Hebrew University of Jerusalem, Jerusalem 91905, 
Israel

Abstract

The location of tide gauges is not random. If their locations are positively (negatively) correlated with SLR, estimates of global SLR will be biased upwards (downwards). We show that the location of tide gauges in 2000 is independent of SLR as measured by satellite altimetry. Therefore PSMSL tide gauges constitute a quasi-random sample and inferences of SLR based on them are unbiased, and there is no need for data reconstructions. By contrast, tide gauges dating back to the 19th century were located where sea levels happened to be rising. Data reconstructions based on these tide gauges are therefore likely to over-estimate sea level rise. 

We therefore study individual tide gauge data on sea levels from the Permanent Service for Mean Sea Level (PSMSL) during 1807 – 2010 without recourse to data reconstruction. Although mean sea levels are rising by 1mm/year, sea level rise is local rather than global, and is concentrated in the Baltic and Adriatic seas, South East Asia and the Atlantic coast of the United States. In these locations, covering 35 percent of tide gauges, sea levels rose on average by 3.8mm/year. Sea levels were stable in locations covered by 61 percent of tide gauges, and sea levels fell in locations covered by 4 percent of tide gauges. In these locations sea levels fell on average by almost 6mm/year.

Related post on a paper by the same first author:

New paper finds the data do not support the theory of man-made global warming [AGW]

Seven examples of how satellite data has been 'adjusted' to exaggerate sea level rise:

Here, here, here, here, here, here, here

How Josh Willis of NASA JPL adjusted the ARGO data from a cooling trend to a warming trend

New paper finds sea levels rose up to 8 times faster & to much higher levels during the last 5 interglacials

A paper published today in Nature Communications finds sea levels naturally rose up to 5.5 meters [18 feet] per century during 5 prior interglacial periods. In addition, the authors finds interglacials "with close to the modern amount of ice on Earth, show rates sea level rise of up to 1 to 1.5 metres per century," which is about 8 times faster than sea levels are rising today with the same levels of ice on Earth [i.e. less than 7 inches per century without acceleration].

Further, in a prior paper by the same authors and using the same data, the authors state that today's sea levels are well within the levels expected from natural variability and that natural variability alone could account for 25 meters more sea level rise than the present:

"Regardless of the uncertainties surrounding the use of any one of the specific scenarios in Fig. 2, it is clear that equilibrium sea level for the present-day [CO2] of 387 ppmv resides within a broad range between 0 and +25 (±5) meters."

and show sea levels during at least 4 prior interglacials over the past 500,000 years were higher than during the present interglacial period [up to 31 feet higher during the last interglacial alone]. Thus, there is no evidence that the [decelerating] sea level rise over the past ~20,000 years is unusual, unprecedented, or unnatural. 

The same data in a prior paper from the same authors shows sea levels during at least 4 prior interglacials were higher than during the present interglacial [at left side of graph]. Green crosses in second graph from top show relative sea level highstand mean and uncertainty.

Study finds global sea levels rose up to five meters per century at the end of the last five ice age cycles

September 25th, 2014 in Earth / Earth Sciences

Credit: Tiago Fioreze / Wikipedia

Land-ice decay at the end of the last five ice-ages caused global sea-levels to rise at rates of up to 5.5 metres per century, according to a new study. [5.5 meters/century is 31 times faster than current sea level rise]

An international team of researchers developed a 500,000-year record of sea-level variability, to provide the first account of how quickly sea-level changed during the last five ice-age cycles.

The results, published in the latest issue of Nature Communications, also found that more than 100 smaller events of sea-level rise took place in between the five major events.

Dr Katharine Grant, from the Australian National University (ANU), Canberra, who led the study, says: "The really fast rates of sea-level rise typically seem to have happened at the end of periods with exceptionally large ice sheets, when there was two or more times more ice on the Earth than today.

"Time periods with less than twice the modern global ice volume show almost no indications of sea-level rise faster than about 2 metres per century. Those with close to the modern amount of ice on Earth, show rates of up to 1 to 1.5 metres per century."

Co-author Professor Eelco Rohling, of both the University of Southampton and ANU, explains that the study also sheds light on the timescales of change. He says: "For the first time, we have data from a sufficiently large set of events to systematically study the timescale over which ice-sheet responses developed from initial change to maximum retreat."

"This happened within 400 years for 68 per cent of all 120 cases considered, and within 1100 years for 95 per cent. In other words, once triggered, ice-sheet reduction (and therefore sea-level rise) kept accelerating relentlessly over periods of many centuries."

Professor Rohling speculates that there may be an important lesson for our future: "Man-made warming spans 150 years already [No - according to the IPCC, there was no significant man-made warming prior to 1950] and studies have documented clear increases in mass-loss from the Antarctic and Greenland ice sheets. Once under way, this response may be irreversible for many centuries to come."

The team reconstructed sea-levels using data from sediment cores from the Red Sea, an area that is very sensitive to sea-level changes because it's only natural connection with the open (Indian) ocean is through the very shallow (137 metre) Bab-el-Mandab Strait. These sediment samples record wind-blown dust variations, which the team linked to a well-dated climate record from Chinese stalagmites. Due to a common process, both dust and stalagmite records show a pronounced change at the end of each ice age, which allowed the team to date the sea-level record in detail.

The researchers emphasise that their values for sea-level change are 500-year averages, so brief pulses of faster change cannot be excluded.

More information: "Sea-level variability over five glacial cycles" Nature Communications, DOI: 10.1038/ncomm6076

___________________________________________

Of course, the alarmists at NBC News have managed to spin this paper to suggest "scary" sea level rise is your fault and spinning out of control, failing to mention it has been decelerating for the past 20,000 years, and with no evidence of any man-made influence [i.e. no acceleration]. 

New paper finds sea levels were significantly higher during past interglacials

A paper published today in Quaternary Research finds sea levels on the island of Curaçao [southern Caribbean] during the last interglacial were up to 9 meters higher than the present, and that during another interglacial period 400,000 years ago sea levels were up to 20 meters higher than the present. According to the paper, these significantly higher sea levels during prior interglacials "require major ice sheet loss from Greenland and Antarctica." The authors determine sea levels by dating fossilized reefs that are presently located high above current sea levels [photo below]. The paper also shows sea levels in the Red Sea were up to ~8 meters higher than the present within the past 5,000 years of the current interglacial, and up to ~12 meters higher than the present during the last interglacial. This and many other papers debunk claims by climate alarmists that recent sea level rise is unprecedented, unnatural, or accelerated. In fact, sea levels rose at a constant rate without acceleration during the 20th century, and have decelerated since 2005 to a rate of only ~1.2 mm/yr [less than 5 inches per century].

Top graph shows sea levels relative to the present during 3 prior interglacials. Bottom graph shows the Red Sea levels for comparison.

Fossilized reefs [shown by dotted lines] formed when sea levels were much higher than the present.

Sea-level history of past interglacial periods from uranium-series dating of corals, Curaçao, Leeward Antilles islands

• Daniel R. Muhs^a, , , 
• John M. Pandolfi^b, , 
• Kathleen R. Simmons^a, , 
• R. Randall Schumann^a, 

• ^a U.S. Geological Survey, MS 980, Box 25046, Federal Center, Denver, CO 80225, USA
• ^b Australian Research Council Centre of Excellence for Coral Reef Studies and School of Biological Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia

• http://dx.doi.org/10.1016/j.yqres.2012.05.008, How to Cite or Link Using DOI

• Permissions & Reprints

Abstract

Curaçao has reef terraces with the potential to provide sea-level histories of interglacial periods. Ages of the Hato (upper) unit of the “Lower Terrace” indicate that this reef dates to the last interglacial period, Marine Isotope Stage (MIS) 5.5. On Curaçao, this high sea stand lasted at least 8000 yr (~ 126 to ~ 118 ka). Elevations and age of this reef show that late Quaternary uplift rates on Curaçao are low, 0.026–0.054 m/ka, consistent with its tectonic setting. Ages of ~ 200 ka for corals from the older Cortalein unit of the Lower Terrace correlate this reef to MIS 7, with paleo-sea level estimates ranging from − 3.3 m to + 2.3 m. The estimates are in agreement with those for MIS 7 made from other localities and indicate that the penultimate interglacial period was a time of significant warmth, on a par with the present interglacial period. The ~ 400 ka (MIS 11) Middle Terrace I on Curaçao, dated by others, may have formed from a paleo-sea level of + 8.3 to + 10.0 m, or (less likely) + 17 m to + 20 m. The lower estimates are conservative compared to previous studies, but still require major ice sheet loss from Greenland and Antarctica
.

New paper claims after 6,000 year 'pause', sea levels began rising 150 years ago

A new paper published in PNAS finds global sea levels rose up to 8 times faster than the present after the peak of the last ice age ~20,000 years ago, followed by a large deceleration starting ~6,000 years ago to stable levels until "the renewed sea-level rise [beginning] at 100–150 years ago."

Examination of the data from the paper, however, shows the range of proxy sea levels is approximately 10 meters, far too large to discern the tiny ~1.5 mm/yr sea level rise over the past 150 years. The authors instead assume from other published studies of tide gauge measurements that the ~1.5 mm/yr sea level rise over the past 150+ years began at that point in time. Other papers find sea levels rising only 1.1-1.3 mm/yr over the past 203 years, and without acceleration. 

Regardless, even the IPCC concedes that there was no significant anthropogenic influence on climate prior to 1950, thus man is not be responsible for sea level rise beginning 150-200 years ago, at the end of the Little Ice Age. 

The sea level rise over the past ~200 years shows no evidence of acceleration, which is necessary to assume a man-made influence. Sea level rise instead decelerated over the 20th century, decelerated 31% since 2002 and decelerated 44% since 2004 to less than 7 inches per century. There is no evidence of an acceleration of sea level rise, and therefore no evidence of any man-made effect on sea levels. Sea level rise is primarily a local phenomenon related to land subsidence, not CO2 levels. Therefore, areas with groundwater depletion and land subsidence have much higher rates of relative sea level rise, but this has absolutely nothing to do with man-made CO2. 

As this post was being written, WUWT posted on this same journal article, which makes additional recommended points regarding much higher sea levels during prior interglacials, etc. 

Fig. 1. Global sea levels over the past 35,000 years. Horizontal axis is thousands of years before the present [i.e. present at the left side of graph]. Range of proxy studies of sea levels is approximately 10 meters over the past ~15,000 years.

Sea level and global ice volumes from the Last Glacial Maximum to the Holocene

1. Kurt Lambecka,b,1, 
2. Hélène Roubya,b, 
3. Anthony Purcella, 
4. Yiying Sunc, and 
5. Malcolm Sambridgea

Author Affiliations

1. Contributed by Kurt Lambeck, September 12, 2014 (sent for review July 1, 2014; reviewed by Edouard Bard, Jerry X. Mitrovica, and Peter U. Clark)

1. Abstract

Significance

Several areas of earth science require knowledge of the fluctuations in sea level and ice volume through glacial cycles. These include understanding past ice sheets and providing boundary conditions for paleoclimate models, calibrating marine-sediment isotopic records, and providing thebackground signal for evaluating anthropogenic contributions to sea level. From ∼1,000 observations of sea level, allowing for isostatic and tectonic contributions, we have quantified therise and fall in global ocean and ice volumes for the past 35,000 years. Of particular note is that during the ∼6,000 y up to the start of the recent rise ∼100−150 y ago, there is no evidence forglobal oscillations in sea level on time scales exceeding ∼200 y duration or 15−20 cm amplitude.

Abstract

The major cause of sea-level change during ice ages is the exchange of water between ice and ocean and the planet’s dynamic response to the changing surface load. Inversion of ∼1,000 observations for thepast 35,000 y from localities far from former ice margins has provided new constraints on the fluctuation of ice volume in this interval. Key results are: (i) a rapid final fall in global sea level of ∼40 m in < 2,000 y at the onset of the glacial maximum ∼30,000 y before present (30 ka BP); (ii) a slow fall to −134 m from 29 to 21 ka BP with a maximum grounded ice volume of ∼52 × 106 km3 greater than today; (iii) after an initial short duration rapid rise and a short interval of near-constant sea level, the main phase of deglaciation occurred from ∼16.5 ka BP to ∼8.2 ka BP at an average rate of rise of 12 m⋅ka−1 punctuated by periods of greater, particularly at 14.5–14.0 ka BP at ≥40 mm⋅y−1 (MWP-1A), and lesser, from 12.5 to 11.5 ka BP (Younger Dryas), rates; (iv) no evidence for a global MWP-1B event at ∼11.3 ka BP; and (v) a progressive decrease in the rate of rise from 8.2 ka to ∼2.5 ka BP, after which ocean volumes remained nearly constant until the renewed sea-level rise at 100–150 y ago, with no evidence of oscillations exceeding ∼15–20 cm in time intervals ≥ 200 y from 6 to 0.15 ka BP.

New paper finds California sea levels up to 66 feet higher than present during last interglacial

A paper published today in Quaternary Science Reviews finds the tectonic uplift rates of the Channel Islands in California are "are much lower than reported earlier" and "are similar to most other parts of coastal California."

The authors also find uplift rates are similar between the Channel Islands, Barbados, and the Florida Keys, and were only ~0.1-0.2 mm/year over the past ~15,000 years, but began to level off to rates of less than half that around 10,000 years ago to the present sea levels.

The University of Colorado, however, adds a highly controversial glacial isostatic adjustment adjustment of 0.3mm/yr to global sea level rise, which may be exaggerated and artificially increasing estimates of sea level rise due to thermal expansion or ice melt. 


The paper also shows that sea levels of the Channel Islands were naturally 20 meters [66 feet] higher during the last interglacial ~120,000 years ago. The paper joins many others demonstrating sea levels during at least 4 prior interglacials over the past 500,000 years were higher than during the present interglacial period [up to 31 feet higher during the last interglacial alone]. Thus, there is no evidence that the [decelerating] sea level rise over the past ~20,000 years is unusual, unprecedented, or unnatural.

Figure from the paper showing uplift of Channel Islands, Florida Keys, and Barbados was ~0.1-0.2mm/yr from ~15,000-10,000 years ago and decelerated to less than half that rate over the past 10,000 years. The figure also shows that sea levels of the Channel Islands were naturally 20 meters [66 feet] higher during the last interglacial ~120,000 years ago. 

The positive global sea level rise trend from satellite altimetry is almost entirely due to an apparent huge wind-driven "bulge" located in the Western equatorial Pacific region. Conversely, all areas shown in blue have experienced a drop in altimetric sea levels [different from relative sea levels which are more dependent upon land height changes] from 1993-2010, including most of the East and West coasts of North and South America. This data is after addition of the likely exaggerated GIA of 0.3mm/yr.

Global sea levels have been naturally rising for ~20,000 years and have decelerated over the past 8,000 years, decelerated over the 20th century, decelerated 31% since 2002 and decelerated 44% since 2004 to less than 7 inches per century. There is no evidence of an acceleration of sea level rise, and therefore no evidence of any effect of mankind on sea levels. Sea level rise is primarily a local phenomenon related to land subsidence, not CO2 levels. Therefore, areas like Miami, Florida and the Florida Keys which are built on soft limestone have higher rates of relative sea level rise, but this has absolutely nothing to do with man-made CO2. 

Coastal tectonics on the eastern margin of the Pacific Rim: late Quaternary sea-level history and uplift rates, Channel Islands National Park, California, USA

• Daniel R. Muhs^a, , , 
• Kathleen R. Simmons^a, 
• R. Randall Schumann^a, 
• Lindsey T. Groves^b, 
• Stephen B. DeVogel^c, 
• Scott A. Minor^a, 
• DeAnna Laurel^d

•

The 2nd marine terrace on the northern Channel Islands is ∼120 ka (U-series, coral).

•

Tectonic uplift rates on these islands are 0.12–0.20 m/ka [meters/1000 years] in the late Quaternary.

•

Uplift rates for the northern Channel Islands are much lower than reported earlier.

•

Differences in uplift rate estimates are due to considerations of GIA effects.

•

Channel Islands uplift rates are similar to most other parts of coastal California.

---

Abstract

The Pacific Rim is a region where tectonic processes play a significant role in coastal landscape evolution. Coastal California, on the eastern margin of the Pacific Rim, is very active tectonically and geomorphic expressions of this include uplifted marine terraces. There have been, however, conflicting estimates of the rate of late Quaternary uplift of marine terraces in coastal California, particularly for the northern Channel Islands. In the present study, the terraces on San Miguel Island and Santa Rosa Island were mapped and new age estimates were generated using uranium-series dating of fossil corals and amino acid geochronology of fossil mollusks. Results indicate that the 2nd terrace on both islands is ∼120 ka and the 1st terrace on Santa Rosa Island is ∼80 ka. These ages correspond to two global high-sea stands of the Last Interglacial complex, marine isotope stages (MIS) 5.5 and 5.1, respectively. The age estimates indicate that San Miguel Island and Santa Rosa Island have been tectonically uplifted at rates of 0.12–0.20 m/ka [meters/1000 years] in the late Quaternary, similar to uplift rates inferred from previous studies on neighboring Santa Cruz Island. The newly estimated uplift rates for the northern Channel Islands are, however, an order of magnitude lower than a recent study that generated uplift rates from an offshore terrace dating to the Last Glacial period. The differences between the estimated uplift rates in the present study and the offshore study are explained by the magnitude of glacial isostatic adjustment (GIA) effects that were not known at the time of the earlier study. Set in the larger context of northeastern Pacific Rim tectonics, Channel Islands uplift rates are higher than those coastal localities on the margin of the East Pacific Rise spreading center, but slightly lower than those of most localities adjacent to the Cascadia subduction zone. The uplift rates reported here for the northern Channel Islands are similar to those reported for most other localities where strike-slip tectonics are dominant, but lower than localities where restraining bends (such as the Big Bend of the San Andreas Fault) result in crustal shortening.

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

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 above graph with a much more compressed scale, 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 ~41,000 years from ~1 million to ~2.7 million years ago. 

The primary purpose of the paper is to help solve the mystery of what causes ice ages, yet it 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 about
Date: April 16, 2014

Source: University of Southampton

Summary: 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

• Affiliations
• Contributions
• Corresponding author

Nature

 

(2014)

 

doi:10.1038/nature13230

Received

 

13 November 2013 

Accepted

 

04 March 2014 

Published online

 

16 April 2014

Article tools

• Abstract• 
• References• 
• Author information• 
• Extended data figures and tables• 
• Supplementary information•
• Comments

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.