New paper claims after 6,000 year ‘pause’, sea levels began rising 150 years ago
|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.|
Contributed by Kurt Lambeck, September 12, 2014 (sent for review July 1, 2014; reviewed by Edouard Bard, Jerry X. Mitrovica, and Peter U. Clark)
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.
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.