ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01073.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01074.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01075.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The remote Pitcairn Group in the South Pacific Ocean comprises a volcanic island (Pitcairn Island), two low coral atolls (Oeno, Ducie) and a raised coralline island (Henderson Island). The geological history of these islands, on anomalously thin oceanic lithosphere, is related to the development of two subparallel island chains (Oeno‐Henderson‐Ducie; Pitcairn) associated with intra‐Pacific plate ‘hotspot’ activity; the surface manifestation of this activity has been partly determined by structural lineations in the plate inherited from past plate history. The climate of the Pitcairn Islands is determined by the position of the subtropical high pressure system and the South Pacific Convergence Zone. Variations in the strength of this atmospheric circulation system, measured by changes in the Southern Oscillation index of pressure difference, provide a partial explanation of the long‐term variability of mean annual rainfall at Pitcairn Island. Knowledge of past climates in the Pitcairn Group remains speculative. Maps of the Pitcairn Islands and a report of climate at Henderson Island (2/91‐1/92) are included

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01076.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Henderson Island is an emergent limestone island. It rises to 33.5 m above modern sea‐level (MSL) from a sea‐floor depth of about 3500 m and conforms to the pattern of an elevated atoll, although no field evidence was found pertaining to the pre‐atoll volcanic history of the island. The emergence of this coral atoll can be explained by lithospheric flexure processes subsequent to the emplacement of the Pitcairn Island volcano, built by two phases of volcanism (estimated at 855 and 540 kyr by K‐Ar dating). U‐Th dates obtained from Henderson Island indicate that the majority of the presently visible fossil corals have an age between 404‐225 kyr. Henderson Island first became emergent above MSL when sea level dropped subsequent to 380 kyr, as the period 440‐380 is thought to have been characterized by sea level at least several metres above MSL in the Central Pacific. As a result Henderson Island would have become subaerially exposed from 380 kyr onwards. The uplift rate of Henderson Island is approximately 0.093‐0.10 mm/yr indicating that flexure‐induced uplift component above MSL commenced between 360‐335 kyr, 500 kyr after the initial, and 190 kyr after the last phase of construction of the Pitcairn volcano. The time‐lag following the loading of the Pitcairn volcano and the present continuation of uplift on Henderson support the theory that the lithosphere behaves in a visco‐elastic manner. Field relations and U‐Th dates indicate three main periods of reef development: (1) A prolific reef‐building period (440‐380 kyr[Unit 1]and 330‐300 kyr[Units 2&3])dominated by large, stout branching coral colonies; (2) A shorter period of reef growth (285‐275 kyr[Unit 4])dominated by well‐formed largein situcoral colonies andTridacna maxima;(3) A less prolific period of reef growth (230‐215 kyr[Unit 5])dominated by platy corals enveloping the previous lithologies below 19.6 m. The absence of dateable material from the last interglacial, oxygen isotope substage 5.5 (= 5e) at Henderson Island is in marked contrast to the Late Pleistocene reefs in the southern Cook Islands where reefs of substage 5.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01077.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Henderson Island, in the Pitcairn Group, preserves a Pleistocene atoll physiography with the rim of the raised reef structure, supporting spur and groove topography, enclosing a central lagoon. Excellent preservation of coral reef communities occurs along the ancient atoll rim and within the central lagoon. The previously interpreted depositional nature of the fossil atoll structure is herein corroborated with geomorphologic and stratigraphic evidence from previously un‐visited portions of the island. Stratigraphic and lateral facies relationships indicate a physiographic zonation which includes spur and grooves, outer reef flat, lagoon margin, and an interior lagoon with patch reefs. Thein situoccurrence and zonation of reef coral communities around the periphery and within the interior of the island appear to reflect the original physiography of the atoll lagoon, with the most pronounced reef development on the SE side of the original atoll. Stratigraphic units which comprise the raised atoll lagoon structure represent different time intervals, so the atoll lagoon structure formed during various sea level fluctuations. The modern atolls of the Pitcairn Group, Oeno and Ducie, provide some comparisons (similarities and differences) with the fossil lagoon on top of Henderson Islan

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01078.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

vascular plant flora of the Pitcairn Islands, south‐central Pacific Ocean, is described based on extensive new collections made in 1991 and previously published records. Two vascular plants occur on Ducie Atoll; one(Pemphis acidula)is a new record. Sixty‐three native vascular plants occur on Henderson, of which nine are endemic;Canavalia rosea, Operculina lurpethum, Psilotum nudumandSolanum americanumare new records for the island. Oeno Atoll has 16 native vascular plants; the single endemic(Bidens hendersonensisvar.oenoensis)was not found in 1991 despite careful searches.Triumfetta procumbenswas new for Oeno. Sixty‐six native vascular plants have now been recorded from Pitcairn Island, there are two endemic ferns and seven endemic angiosperms in this number. A number of non‐native taxa were new to Pitcairn. Some of the previously described taxa could not be found on Pitcairn, probably because they are very rare and only a small amount of time was spent collecting on Pitcairn. Many of the Pitcairn taxa are threatened by the spread of introduced species, especiallySyzygium

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01079.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The vegetation of the raised coralline Henderson Island and Oeno Atoll (Pitcairn Group, south‐central Pacific Ocean) is described from cover‐abundance values of the vascular flora sampled in 10 times 10 m quadrats. Exploratory data analysis by detrended correspondence analysis and two‐way indicator species analysis was used to summarize the resulting data matrices for each island, and to aid definition of vegetation types. For Henderson, six major vegetation communities are described, which are often closely linked to geomorphology: beachfront, embayment forests, open limestone scrub, cliff and ledge, exposed cliff top, and plateau forests. For Oeno, four main vegetation communities are described: open sandy littoral,Argusiascrub, closed forest, and coconut grove. For each island, the main vegetation types were further subdivided into a number of communities depending on the proportions of various taxa. Brief qualitative descriptions of the vegetation of Ducie and Pitcairn are also given. Anthropogenic communities, some of which are highly invasive, are widespread on Pitcairn. Adequate conservation measures must be given to all islands in the Pitcairn Group; this will protect not only the endemic‐rich and possibly unique plateau forests of Henderson, but also the species‐poor and scientifically important analogues of vegetation types which occur elsewhere in the Pacifi

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01080.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01081.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Over 13 months we studied the diet of the fruit dovePtilinopus insularis, endemic to the exceptionally remote South Pacific island of Henderson. Nineteen plant species were recorded in the diet by faecal analysis and direct observation. The fruit ofProcris pedunculata(Urticaceae) was the most common food. When it was unavailable, the doves turned to the young shoots of the fernPhymatosorus scolopendria.Subject to a maximum diameter of about 18 mm, the doves ate nearly all types of available fruit. By combining the diet studies with studies of plant phenology we were able to assess which, of the fruits available, were preferred. The doves preferred the larger fruit. Given that the fruit dove today eats nearly all available fruit species, we ponder on how it co‐existed with at least two other pigeon species that formerly lived on Henderson Islan

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1995.tb01082.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY