To review our material in any detail, it is important to understand the significance of sea level raise during the current Holocene epoch. Since the Holocene Start, or about 12,000 years ago, sea levels around the world rose an average of 80 meters or 265'. Most of that increase, or about 260', occurred over a 5,000 year period between 12,000 and 7,000 years ago.
Some 'leveling', or trigger event just over 7,000 years ago, flattened out that rapid increase in sea level.
The data represented on the above chart, has been collected from 8 locations around the globe. Variations in sea level rise from the Western Atlantic and the South Pacific are most notable. The figures are based on data from Fleming et al. 1998, Fleming 2000, & Milne et al. 2005. These papers collected data from various reports and adjusted them for subsequent vertical geologic motions, primarily those associated with post-glacial continental and hydroisostatic rebound. The first refers to deformations caused by the weight of continental ice sheets pressing down on the land, the latter refers to uplift in coastal areas resulting from the increased weight of water associated with rising sea levels. It should be noted that because of the latter effect and associated uplift, many islands, especially in the Pacific, exhibited higher local sea levels in the mid Holocene than they do today. Uncertainty about the magnitude of these corrections is the dominant uncertainty in many measurements of Holocene scale sea level change.
The black curve is based on minimizing the sum of squares error weighted distance between this curve and the plotted data. It was constructed by adjusting a number of specified tie points, typically placed every 1 kyr and forced to go to 0 at the modern day. A small number of extreme outliers were dropped. It should be noted that some authors propose the existence of significant short-term fluctuations in sea level such that the sea level curve might oscillate up and down about this ~1 kyr mean state. Others dispute this and argue that sea level change has been a smooth and gradual process for essentially the entire length of the Holocene. Regardless of such putative fluctuations, evidence such as presented by Morhange et al. (2001) suggests that in the last 10 kyr sea level has never been higher than it is at present.
The following illustration is a Holocene Sea Level chart plotting sea level over the past 9,000 years
Of significance, is the Jamaica or 'Caribbean Plain' sea level plot, shown in light turquoise. We are using the Jamaica plots, because the plot readings are the closest to our Atlantic and Gulf coasts. This Jamaica plots show an average sea level increase of about 5' 5" between 7,000 and 5,000 ybp. From that point forward, sea level has been relatively stable, with less than 1' increase.
There appears to have been some 'trigger' event at just before 7,000 ybp, that literally stopped the rapid sea level raise. Over the next 1,000 years, sea level raises 'flattened out' to about 3' at 6,000 ybp. From that point to 5,000 ybp, the raise was less than 2', and in the last 5,000 years, sea level has been relatively constant.
Using sea level as a dating mechanism is valid when a non-natural occurring harbor, canal, channel, feature, contour or artifact situated on a tidal shelf can be identified as having been built or created when that area was above sea level.
1. Underwater 'harbors' not connected to any current shoreline. Recognizing the purpose for a 'harbor' is to connect a shore based area with major, or ocean going water based transportation systems.
2. Underwater canals, harbors, or channels that show a substantial 'berm' or residue along its edge. This feature is a result of dredging where the residue of refuse is discharged along the bank. This does not occur with an underwater dredging process, where the refuse is piped from the dredge head, generally on a barge, or floating above water, to a refuse or 'tailing' pile on shore, often at some distance from the dredge rig.
3. Channels and canals that have contiguous major sections both above and below sea level.
Most information on this website is supported by artifacts and construction on the Secondary Tidal Plain level, indicating its build and use dates to be no earlier than the Tertiary Tidal Shoulder of 7,200 ybp, and no later than the Secondary Tidal Shoulder of 5,900 years ago.