- Email: [email protected]
Aperçu sur les résultats de deux plongées effectuées dans le ravin de Puerto-Rico par le bathyscaphe Archimède
1094
Oceanographic Abstracts
P~RJ~s J. M. 1965. Apereu sur les r6sultats de deux plong~es effectu6es dans le ravin de PuertoRico par le bathyscaphe Archimdde. Deep-Sea Res., 12 (6): 883-891. Two dives, to depths of 7,300 m and 3,100 m were performed on the southern side of the Puerto-Rico trench, chiefly for biological observations. The deposition of organic material is more considerable at 7,300 m (where a process of decantation seems to occur) than at 3,100 m. Limestone flags observed at 3,100 m showed signs of active present-day corrosion. Plankton study is made difficult, when the bathyscaphe dives to great depths, by the speed o f descent (about 1 m/sec). During the dive to 7,300 m the density of the plankton showed a marked diminution towards 6,600 m, that is, passing from the abyssopelagic to the hadopelagic zone. The increase in density o f the plankton usually observed in the last few metres above the bottom seemed slight, although many amphipods (Stegocephalids?) were seen. During the dive to 3,100 m numbers of a medusa (Aglantha?) were seen between 1,500 and 2,800 m; below 2,900 m plankton was virtually absent. Only the benthic epifauna could be studied, as the bottom sampler failed to work. At 7,300 m the community was characterized by the abundance of liparidid fish (Careprotus?: about 200 individuals); fair numbers of holothurians were also seen (Synallactidae and Myriotrochus), several Nematocarcinus, and. a large asellote isopod, probably of an undescribed species. At 3,100 m a total absence of epifauna was noted on hard substratum, and a synallactid holothurian was dominant on muddy sand; the fishes were very rare. General remarks on the use of the bathyscaphe, in its present state, for biological work are given. PHLEGER FRED B, 1965. Sedimentology of Guerrero Negro Lagoon, Baja California, Mexico. In: Submarine geology and geophysics, Colston Papers, W. F. Whittard and R. Bradshaw, editors, Butterworth's, London, 17: 205-235. Guerrero Negro Lagoon is one of a group of three coastal lagoons on the Pacific Coast of Baja California which also includes Ojo de Liebre and Manuela Lagoons. The area has an arid climate, vegetation is sparse and there are no streams flowing into the lagoons. There is considerable wind usually from a northwesterly direction. The lagoonal barrier is composed o f fine sand with abundant shell and Foraminiferida, and is mostly covered with barchan dunes. The lagoonal floor has channels separated from extensive tidal flats by relatively steep channel slopes. Extensive marine marsh is populated with Spartina down to about + 3 ft and succeeded by a Salicornia assemblage at about + 4 to 4½ ft. Channel and marsh foraminiferal populations are distinct. The deepest channels are in the lower lagoon. An inlet delta extends 2-2½ miles seawards from the inlet. Maximum tidal range is about 9 ft and average range is about 5 ft. Tides generally are 20-40 rain later at about 5 miles within the lagoon than at the inlet. Maximum tidal currents in the channels vary from approximately 4½ knots at the hydraulic entrance to 1 knot or less in inner lagoonal channels. Sediment is transported into the lagoon mainly by wind from bordering dunes and is distributed within the lagoon by tidal currents. Deposition occurs on the intertidal flats and marshes on the flood-tide, and on the ebb-tide there is scour from the tidal flats and channel-slopes. Sediment in suspension in the lower lagoon during the ebb-tide tends to be deposited on the seaward edge o f the inlet delta. The hydraulic inlet is moving northwards due to current-scour on the northern side and related bar-encroachment on the south. The inlet area apparently has migrated northwards about 2 miles since the formation of the lagoon. Old storm-berms occur on the lagoonal barrier at 3000-5000 ft inland and separated by old inter-berm beaches. Radiocarbon dates on Donax shells suggest an age of about 2000 B.P. for the oldest berm. Older radiocarbon dates are believed to be due to contamination with older Donax shells transported from the near shore zone by storm waves at the time the berms were formed. It is suggested that contamination with younger shell is due to overwash transport at time of formation of younger berms. The evidence from this area indicates that sea-level has been at approximately its present position for about 2000 years and that the barrier has prograded seawards 5000 ft during that time. The surface on which post-glacial sediments were deposited slopes seawards at about 5 ft mile and the sediments are 35--40 ft thick at the barrier. Cores through most o f the barrier-deposits show sediments like those at the present surface. It is suggested that the origin of the lagoon was by formation of a sand-barrier 6000-7000 B.P. when sea-level was approximately 30--40 ft lower than now. As sea-level rose the barrier built upwards and prograded seawards due to beach construction by waves, and the landward side of the barrier was raised to the beach-level by wind-blown sand. PICHON M., 1964. Contribution gt l'6tude de la repartition des Madr6poraires sur le r6cif de Tul6ar, Madagascar. Reel. Tray. Stn. mar. Endoume. hors sdr., Suppl. No. 2: 79-203. (Tray. Sta. Mar.,
Tuldar).
This work is an attempt to describe the reef-system (barrier reef) of Tul6ar (Madagascar), by methods o f benthic bionomy suggested by P6r~s and Picard. A short geomorphological description is given of the various reef regions, each being specially studied in a particular chapter: Seaward (or outer) slope, outer reef flat, boulder rampart, outer reef flat creeks, friable flat, ponds in the inner flat, phanerogamous flat, landward (or inner) slope. S°meindicati°ns are given ° fthe ee°l°gical c°nditi°ns" The animals and the distribution o f the Madreporaria are then examined in some detail. The distribution of Madreporaria, and the zonation on the reef o f Tul&ar are considered. Some
Oceanographic Abstracts
P~RJ~s J. M. 1965. Apereu sur les r6sultats de deux plong~es effectu6es dans le ravin de PuertoRico par le bathyscaphe Archimdde. Deep-Sea Res., 12 (6): 883-891. Two dives, to depths of 7,300 m and 3,100 m were performed on the southern side of the Puerto-Rico trench, chiefly for biological observations. The deposition of organic material is more considerable at 7,300 m (where a process of decantation seems to occur) than at 3,100 m. Limestone flags observed at 3,100 m showed signs of active present-day corrosion. Plankton study is made difficult, when the bathyscaphe dives to great depths, by the speed o f descent (about 1 m/sec). During the dive to 7,300 m the density of the plankton showed a marked diminution towards 6,600 m, that is, passing from the abyssopelagic to the hadopelagic zone. The increase in density o f the plankton usually observed in the last few metres above the bottom seemed slight, although many amphipods (Stegocephalids?) were seen. During the dive to 3,100 m numbers of a medusa (Aglantha?) were seen between 1,500 and 2,800 m; below 2,900 m plankton was virtually absent. Only the benthic epifauna could be studied, as the bottom sampler failed to work. At 7,300 m the community was characterized by the abundance of liparidid fish (Careprotus?: about 200 individuals); fair numbers of holothurians were also seen (Synallactidae and Myriotrochus), several Nematocarcinus, and. a large asellote isopod, probably of an undescribed species. At 3,100 m a total absence of epifauna was noted on hard substratum, and a synallactid holothurian was dominant on muddy sand; the fishes were very rare. General remarks on the use of the bathyscaphe, in its present state, for biological work are given. PHLEGER FRED B, 1965. Sedimentology of Guerrero Negro Lagoon, Baja California, Mexico. In: Submarine geology and geophysics, Colston Papers, W. F. Whittard and R. Bradshaw, editors, Butterworth's, London, 17: 205-235. Guerrero Negro Lagoon is one of a group of three coastal lagoons on the Pacific Coast of Baja California which also includes Ojo de Liebre and Manuela Lagoons. The area has an arid climate, vegetation is sparse and there are no streams flowing into the lagoons. There is considerable wind usually from a northwesterly direction. The lagoonal barrier is composed o f fine sand with abundant shell and Foraminiferida, and is mostly covered with barchan dunes. The lagoonal floor has channels separated from extensive tidal flats by relatively steep channel slopes. Extensive marine marsh is populated with Spartina down to about + 3 ft and succeeded by a Salicornia assemblage at about + 4 to 4½ ft. Channel and marsh foraminiferal populations are distinct. The deepest channels are in the lower lagoon. An inlet delta extends 2-2½ miles seawards from the inlet. Maximum tidal range is about 9 ft and average range is about 5 ft. Tides generally are 20-40 rain later at about 5 miles within the lagoon than at the inlet. Maximum tidal currents in the channels vary from approximately 4½ knots at the hydraulic entrance to 1 knot or less in inner lagoonal channels. Sediment is transported into the lagoon mainly by wind from bordering dunes and is distributed within the lagoon by tidal currents. Deposition occurs on the intertidal flats and marshes on the flood-tide, and on the ebb-tide there is scour from the tidal flats and channel-slopes. Sediment in suspension in the lower lagoon during the ebb-tide tends to be deposited on the seaward edge o f the inlet delta. The hydraulic inlet is moving northwards due to current-scour on the northern side and related bar-encroachment on the south. The inlet area apparently has migrated northwards about 2 miles since the formation of the lagoon. Old storm-berms occur on the lagoonal barrier at 3000-5000 ft inland and separated by old inter-berm beaches. Radiocarbon dates on Donax shells suggest an age of about 2000 B.P. for the oldest berm. Older radiocarbon dates are believed to be due to contamination with older Donax shells transported from the near shore zone by storm waves at the time the berms were formed. It is suggested that contamination with younger shell is due to overwash transport at time of formation of younger berms. The evidence from this area indicates that sea-level has been at approximately its present position for about 2000 years and that the barrier has prograded seawards 5000 ft during that time. The surface on which post-glacial sediments were deposited slopes seawards at about 5 ft mile and the sediments are 35--40 ft thick at the barrier. Cores through most o f the barrier-deposits show sediments like those at the present surface. It is suggested that the origin of the lagoon was by formation of a sand-barrier 6000-7000 B.P. when sea-level was approximately 30--40 ft lower than now. As sea-level rose the barrier built upwards and prograded seawards due to beach construction by waves, and the landward side of the barrier was raised to the beach-level by wind-blown sand. PICHON M., 1964. Contribution gt l'6tude de la repartition des Madr6poraires sur le r6cif de Tul6ar, Madagascar. Reel. Tray. Stn. mar. Endoume. hors sdr., Suppl. No. 2: 79-203. (Tray. Sta. Mar.,
Tuldar).
This work is an attempt to describe the reef-system (barrier reef) of Tul6ar (Madagascar), by methods o f benthic bionomy suggested by P6r~s and Picard. A short geomorphological description is given of the various reef regions, each being specially studied in a particular chapter: Seaward (or outer) slope, outer reef flat, boulder rampart, outer reef flat creeks, friable flat, ponds in the inner flat, phanerogamous flat, landward (or inner) slope. S°meindicati°ns are given ° fthe ee°l°gical c°nditi°ns" The animals and the distribution o f the Madreporaria are then examined in some detail. The distribution of Madreporaria, and the zonation on the reef o f Tul&ar are considered. Some