Observational facts from the Maldives, Goa and Bangladesh in the Indian Ocean and from Fiji and New Caledonia in the Pacific record a high sea level in the 17th century, a low sea level in the 18th century, a high sea level in the early 19th century and a stable sea level in the last 50 - 70 years. This cannot be understood in terms of glacial eustasy (or in terms of steric effects or tectonics), only in terms of rotational eustasy. The present paper gives a summary of the observational facts behind the formulation of the novel concept of rotational eustasy. It reveals a common trend of sea level changes, which is opposed to the sea level changes in the northern hemisphere, and the global climatic changes in general. Rotational eustasy offers a logical explanation.
The theory of rotational eustasy emerged as a direct consequence of observational facts from numerous sites on a number of key areas in the Indian Ocean and the Pacific. The data obtained revealed that there was a missing factor in our understanding of the cause of sea level changes; the concepts of glacial eustasy and thermal water expansion were not able to explain the variations in sea level observed (nor were local tectonics). The additional factor needed was termed “rotational eustasy” and its physical understanding has been presented in a special paper of this journal [1] .
A new theory stands and falls with the quality of the basic observational facts. Therefore, this paper presents a summary of available facts upon which the theory of rotational eustasy is based. Previously, each region was presented separately. It soon became obvious that there was a common trend in the sea level changes during the last 500 years within the Indian Ocean and the Pacific, and that this trend was very different from the records of the northern hemisphere and global climate in general. This paper highlights the facts (region for region) upon which the concept of rotational eustasy is based [1] .
2. Eustatic Test Areas in Europe
The Stockholm area, the Kattegatt Sea and the Amsterdam region constitute excellent test areas for the regional eustatic component, because the absolute crustal component is known in detail (Stockholm going up by 4.9 mm/yr, the whole of the Kattegatt area being covered by absolute crustal movement documentation with the zero isobase fixed for the last 8000 years in the Great Belt area, the Amsterdam area subsiding at a rate of 0.4 mm/yr). The absolute eustatic component can be firmly fixed at +1.05 ± 0.15 [2] [3] [4] [5] [6] .
The regional eustatic component of the US East Coast seems to be in a similar order of magnitude [7] [8] .
3. The Maldives
In 2000 we initiated the International Sea Level Project in the Maldives. After 6 expeditions, careful documentation of coastal morphology in different dynamic settings, stratigraphy, leveling and 57 C14-dates, a quite comprehensive picture was established of the sea level changes during the last 5000 years [9] - [16] .
Figure 1 summarizes the main steps of the sea level changes during the last 500 years: a +50 - 60 cm high sea level in the 17th century (Figure 2), a low sea level in the 18th century with submarine peat (Figure 3), and a 10 - 20 cm drop at around 1970 (Figure 4).
4. Goa, India
In Goa, it was possible to establish a very comprehensive record of sea level changes during the last 500 years [15] by applying a combination of shore morphology, stratigraphy, biological index levels, archaeological buildings, old harbours, the scenery in an old painting, historical notes and tide gauge records. The database is summarized in Figure 5.
There is a clear +60 cm high sea level dated at 1615 ± 12 cal. yrs BP (Figure 6), a submarine building at about −1 m dated at 1700-1750 AD (Figure 7), a 20 cm drop in sea level at about 1960 (Figure 8), and a stable sea level over the last 60 (Figure 5).
5. Bangladesh
The Bangladesh sea level record is summarized in Figure 9 [16] [17] [18] . It shows the occurrence of a clear low sea level stage in the late 18th to 17th century [18] and a drop in sea level of about 10 - 20 cm at about 1960 [17] . There seems also to be stratigraphical records of the 1733 tsunami during the formation of the low sea level deposits [12] .
6. The Fiji Islands
In the Yasawa Islands of the Fiji Islands, we undertook extensive shore morphological analyses and dating [16] [19] [20] giving a detailed record of the sea level changes during the last 500 years (Figure 10).
There is a clear +70 cm high sea level record dated at the late 16th to late 17th century (Figure 11), a low sea level in the 18th century reaching −100 - 70 cm (Figure 12), a +30 cm in the early 19th century (Figure 13), a stable sea level over the last 150 (Figure 13) years with a 10 - 20 cm lowering in the late 20th century and perfectly stable sea level conditions for the last 20 - 60 years forcing coral growth into microatolls (Figure 14).
7. Ouvéa Island in New Caledonia
On the Ouvéa Island there are excellent records of the +70 cm sea level of the 17th century (Figure 15, with additional illustrations in [1] . There is also morphological evidence of the absence of a present sea level rise [21] . Figure 16 shows the +70 cm shore, the sub-recent +20 cm level now abandoned and overgrown, and the present stable sea level. A recent 20 cm fall in sea level (in the 1950s) is well documented in Figure 17.
8. Some Other Sites
The absence of a present-day rise in sea level is documented from many other sites in the equatorial region of the Indian Ocean and the Pacific. This is the case with the Minicoy Island [7] [15] , St. Paul Island [15] and Qatar [22] in the Indian Ocean, and Tuvalu [11] [23] , Vanuatu [11] , Kiribati [24] [25] and Samoa [26] in the Pacific.
9. Conclusions
The observational facts highlighted above (see also [16] ) document the following sequence of events recorded by multiple records in the Indian Ocean and the Pacific:
1) A +60 - 70 cm high sea level in the late 16th to 17th century, well recorded and dated in the Maldives, Goa, Fiji and New Caledonia.
2) A low sea level (well below the present one) in the 18th century, well recorded and dated in the Maldives, Goa, Bangladesh and Fiji.
3) A +30 cm high sea level in the early 19th century, well recorded in the Maldives, Goa and Fiji (also seen in Ouvéa Island).
4) A stable sea level 10 - 20 cm above the present one in the late 19th to early 20th centuries, well recorded in the Maldives, Goa, Bangladesh, Fiji and New Caledonia.
5) A 10 - 20 cm sea level lowering in 1950-1970, well recorded in the Maldives, Goa, Bangladesh, Fiji and New Caledonia
6) Stable sea level conditions in the last 20 - 60 years, as documented in the Maldives, Goa, Bangladesh, Fiji, New Caledonia and a number of other sites (e.g. Minicoy, St. Paul Island and Qatar in the Indian Ocean, and Tuvalu, Vanuatu, Kiribati and Samoa in the Pacific).
The sea level records are so similar [1] [7] [13] [15] [19] [21] that they can be combined into a common sea level curve of the last 500 years (Figure 18(A)) valid for the equatorial regions of the Indian Ocean and the Pacific. This curve is totally different than the one obtained for the eustatic test areas of northwestern Europe (Figure 18(B)). This can only be understood in terms of rotational eustasy
[19] [20] [21] calling for a separate explanation in terms of physics as presented and further discussed in a separate paper [1] .
Acknowledgements
I thank all colleagues actively involved in the field studies and all local persons so generously assisting us in the field. I am indebted to Pamela Matlack-Klein for skilful linguistic review of the paper.
Conflicts of Interest
The author declares no conflicts of interest regarding the publication of this paper.
Cite this paper
Mörner, N.-A. (2019) Rotational Eustasy as Observed in Nature. International Journal of Geosciences, 10, 745-757. https://doi.org/10.4236/ijg.2019.107042
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