The palynology and sedimentology of a coastal swamp at Awana, Great Barrier Island, New Zealand, from c. 7000 yr B.P. to present

Abstract

Pollen and sediment analysis of two Holocene cores from Awana, Great Barrier Island, shows that at 7000 calibrated yr B P the local swamp was an estuanne salt marsh dominated by Restionaceae By c 6000 yr B P the water table was lower, and a fresh water swamp (Gleichenta-Leptospermum) had replaced the salt marsh Regional coniferhardwood forest c 7000 yr B P was initially co-dominated by Libocedrus and Dacrydmm cupressinum Libocedrus declined from c 6000 yr B P During the period c 6000-c 2500 yr B P , relatively stable environmental conditions ensued with little change in local or regional vegetation Around 2500 yr B P , the swamp surface became drier and was invaded by Dacrycarpus and Laureha swamp forest This forest was subsequently repeatedly disturbed (not by fire), indicating climatic change to drier and windier conditions Ascanna lucida was periodically a major component of swamp forest Disturbance is also recorded in the clastic (mineral) sediments, where beds of sand within finer-grained sediment and peat are interpreted as wind blown material derived from partly devegetated dunes to seaward The presence of the Kaharoa Tephra allows the timing of major Polynesian deforestation at Awana to be reliably dated to c 600 calibrated yr B P In contrast, we see no evidence in the clastic sediment record of disturbance at Awana since Kaharoa time We attribute this to the maintenance of stable dunes by a herb/scrub cover despite nearby fires, or to the presence of scrub or forest buffering the swamp from ablating dunes

A reconstruction of the history of a Holocene sand dune on Great Barrier Island, northern New Zealand, using pollen and phytolith analyses

“…A tephra forms a layer at 12–15 cm with a distinct upper boundary and diffuse lower boundary. Although this tephra was not geochemically analysed, its thickness (3 cm), colour, particle size and stratigraphic position near the surface (12–15 cm) clearly indicates that it is Kaharoa Tephra, which has been geochemically identified at other Awana sites (Horrocks et al. , 1999; Horrocks et al.…”

“…Neither the phytolith nor the pollen record provides direct evidence to indicate the time of deposition of the dune at the site. From sedimentological and pollen data from southern Awana, Horrocks et al . (1999) suggested that local dunes had probably stabilized by c. 6000 cal.…”

“…The southern half of the system lies directly behind dunes while the northern half extends inland into the Awana Stream valley behind coastal hills. The palynology and environmental history of the southern part of the swamp system since c. 7000 yr bp has been described by Horrocks et al . (1999).…”

Last Glacial pollen–climate reconstructions from Northland, New Zealand

“…Previously in Northland, Rotoehu tephra has been documented within lake sediment cores from Lake Omapere (Newnham et al ., ), and in Auckland in carbonaceous muds exposed at Point England (AT2; Alloway et al ., ), in soil cover‐beds close to the present‐day ground surface alongside State Highway 1 at Papatoetoe and more recently in long sediment cores retrieved from Pukaki and Onepoto craters (Newnham et al ., ; Shane and Hoverd, ). Rotoehu tephra has also been reported at Omaha about 60 km north of Auckland (Lorrey and Bostock, 2017) and described from soil and dune cover‐bed sections throughout Coromandel and on Great Barrier Island (Horrocks et al ., , ). The distribution of Rotoehu tephra in the Rotorua and Taupo areas was first presented by Pullar and Birrell () then modified to include 150‐, 120‐ and 100‐mm isopachs drawn across the Auckland–Northland region by Newnham et al .…”

Palaeoenvironment and human impact in modifying vegetation at Mt St John, Auckland Isthmus, New Zealand

“…However, lack of significant charcoal in the lowermost two samples indicates that large-scale deforestation by Polynesians had not occurred in or near the crater at the time of initial swamp formation. The apparent presence of Ascarina pollen in these two samples only may indicate the early Holocene (McGlone & Moar 1977), although this signal is less reliable in northern regions (e.g., Newnham 1992;Horrocks et al 1999).…”