Khoa học và công nghệ biển

Up one level

About the geo-environmental changes and questions of environmental resources in Cua Luc, Ha Long Bay

Up to now, the influences of geo-environmental changes on the environmental resources and the societal - economic development, in the Quang Ninh coastal zone, especially in Cua Luc-Halong Bay have been touched upon by some scientific documents and writen texts of State Organnnics. About these questions, recently one have discussed in some scientific works and conferences. But, practically how was the geologic environment of tltis region changed? How were the environmental resources influenced and regressed? What solutions to the diminution of geo-environmental changes, that have influenced the environmental resources? These questions will be touched upon in this article.

Calculating the 3D current for estuary area

In this paper, some 3D current calculated results in Dinh An estuary are presented . The calculated results are new and interesting. The spatial distributions of component current velocities (u, v, w) and transimition of fresh water to the sea and their mixing ability in the studying area are shown. The buoyance effect due to difference in densities of fresh and sea water and the inertia of river and coastal flows are described. Tidal and river flow phases in calculating process are supposed to be a relatively slable system.

Coastal development and sea level change during holocene in Hai Phong area

In principal, the positive and negative morpho-structures in Haiphong area are developed on inheritable basement of depressed and uplifted zones of neotectonic and recent tectonics. However. the negative morpho-structure on the Bach Dang estuary expands partly to weakly uplifted zones. It is a influence of Holocene eustatic transgression in a coastal landform separated strongly. During Holocene, the coastal development in Haiphong has been regulated by the interaction of tectonic movement, eustatic change in sea level and deposition. There is a quite difference in sedimentary thickness of Holocene formations of Hai Hung (QIV 1-2 hll) and Thai Binh (QIV-3 tb) at the uplifted and downed tectonic zones. In the northeast part, the sedimentary facies are mangrove swamp and tidal flat commonly, and the thin layers of subtidal facies are very limited. In strongly uplifted zones and weakly uplifted zones partly, sediments of these formations belong mostly to the facies of mangrove swamps. All marine terraces included level I of 3-3.5m high and early late Holocene, level II of 4-6m high and middle-middle Holocene and level III of 8-/2m high and lately late Pleistocene. The marine notches in equivalent heights on limestone cliffs are located on the uplifted recent tectonic zone. Five systems of sand beach ridges formed during coastal evolution reflect obviously the relative change in sea level. The first is of 4-6m high and middle-middle Holocene age; The second is of 3-3.5m high and early late Holocene; The third is of 2-2.5m high and middle late Holocene; The fourth is of 2.5-3m high and lately late Holocene; and The fifth is of 3-3.5m high and present time. From them, the third system is the lowest and was formed at about) ky BP. During last 7 ky, the shoreline moves seaward or landward several times that is caused mainly by the relationship between depositional rate and sea level flllctuation as a combination of tectonic movement and eustatic rise. The eustatic change in Holocene sea level in this area was proved to rise up present level. Meanwhile, the coastline change-relative sea level fluctuation has a sinuolls shape on axis of present mean sea level (.MSL) with its amplitude smaller after time. The relatively sea level was highest from + 4-6m above MSL at about 5-6 ky BP. Then, it dropped down 2.5-4m below MSL at about 3-4 ky BP corresponding to period of Ha Long Culture and archeological site of Trang Kenh. After that, it rose lip 3-3.5m above MSLfrom 2-3 ky BP, dropped down I.5m below MSL at abollt I ky BP; and then has been rising up present level. The Viet Khe ancient inhabitants were separated from the Trang Kenh ancient inhabitants by sea ingression from 2-3 ky BP. In late Holocene, the relative sea level was the lowest at about) ky BP when the Red River Delta generally, Haiphong area particularly, was influenced by flooding atthe least degree. Durin the last thousand years, the delta in southwest Haiphong has expanded continuously in the condition of sea level rising, but smaller than deposition in rate. By coastal accretion, at about 0.5-0.7 ky BP. Do Son Island was connected to expanding delta into a peninula. Since that, Bach Dang estuary in the northward Haiphong has been d~veloping on the location offormer delta. All three navy battles on the Bach Dang River from IOth-XIlth centuries happened in deltaic em'ironment when shoreline was far out in the sea, and riverbed was narrower and shallower than those at the present.

Lookback the sea level change in quaternary based on sedimentary research in littoral and shallow sea from Nha Trang to Bac Lieu

To study sea level change in Quaternary one must base on the following factors: - Sedimentary cycles and absolute ages dated by Thermoluminescence method.- Distribution and C14 ages of coral.- Associations of lithofacies distributed in continental shelf and demonstrated ancient coastline caused by regression and transgression. Based on these documents , 5 phases of regression and transgression: Q,', Q1, Q,2-3. Q,3, Q2 can be proposed.

Sea surface heat balance in the sea adjacent to Truong Sa and Phu Quoc islands

In the paper, a well known method for calculation of the sea heat balance developed by A. I. Voikovs Institute of Geophysics, (Russian Federation), is presented. The elements of sea surface heat balance in the sea areas near Truong Sa and Phu Quoc islands were calculated and analysed. The results showed the semilarity of annual variation of the sea surface radiation and the difference of annual variation of heat balance as well as evaporation and interaction of temperature flow with the medium in the two areas. The anomaly of annual variation of the sea surface heat balance elements during July in the sea near Phu Quoc island is probably caused by upwelling phenomena.

The names of the coastal island system of Vietnam

For calling these islands in Viet Nam there are 5 common names to be used: hon, dao, con, Cu lao and da. The author introduces the characteristics on their quantity, area and distribution, and analyses also the process of transformation from the name poullo, Cu lao into hon and dao. The proper names of islands dao have many different meaning.