Holocene Sea Levels
By Ed Caryl
There are many indications that sea level was much higher immediately after the last ice sheets melted 7000 years ago. There were other high-stands in the intervening years. Two sources are presented here that attempt to measure past sea levels.
Most Holocene sea level studies depend on geological and archeological evidence and a good deal of speculation. Two studies were found that have substantial evidence, presented in detail.
The first (Aus K.-E. BEHRE, Probleme der Küstenforschung, Bd.28, Isensee-Verlag, Oldenburg, 2003) was found as second and third hand charts in Frans J.P.M. Kwaad’s paper here, in Dutch, translated with Google Translate. The original Behre papers are behind a paywall, here. Other sources cite Behre, but some cast doubt on his work without offering alternatives.
From the charts, new curves were constructed in Excel so that Post Glacial Rebound (PGR) corrections could be made, and curves compared. Behre never took PGR into account in his work. He was also charting the high water marks, not MSL, so his charts set the present sea level to 1.75 meters. To correct for this, 1.75 meters were subtracted from his data. The data were collected in the stretch of seacoast called the German Bight, the area from Dutch Friesland to Danish Friesland, the south coast of the North Sea, centered on Wilhelmshaven.
I took the Wilhelmshaven PGR uplift figure as the starting point for the correction. PGR changes over time, doubling in about every 2000 years as one goes back to the end of the glacial retreat 7000 years ago.
Figure 1a above
Figure 1b. Both Figures 1a and 1b are from F. J. P. M. Kwaad here. Click for larger view.
The next data are from the Western Pacific, specifically the Yellow River Delta and the Sunda Strait, taken from J. P. Liu et al, 2004, Holocene Development of the Yellow River’s subaqueous delta, North Yellow Sea. Marine Geology, 209(1-4): page 60. This chart describes the sea level rise at the end of the last ice age. Don’t be confused by the reversal in the horizontal axis. In the literature, time can run left to right or right to left. The time scales can also have zero at the birth of Christ, or at the present day.
The data from these charts, with PGR and High Water correction, results are shown in Figure 3:
Figure 3 is a plot of the last 10,000 years of sea level, combining data from figures 1a, 1b, and 2.
In Figure 3, we can see the agreement between the two data sources for the period from 6000 years before present to 10,000 years before present, validating the procedure.
By focusing on the last 8000 years, we can also see the sea level high stands at the Medieval Warm period, the Roman Warm Period, and the Egyptian/Minoan Warm Period as well as the Holocene Climate Optimum after all the great ice sheets melted. These latter two high stands are roughly two meters above the current sea level. The low stands are about one meter below current sea level.
When looking at these, keep in mind that there is a delay between temperature and sea level. That delay depends on the amount of temperature change and the level from which the temperature changed. In Figure 4, the delay seems to average at least 200 years.
In the last 8000 years, sea level has been substantially higher than at present, up to 2 meters or more higher in two periods four to seven thousand years ago. Sea level during the Holocene has been falling since that period.