Rewi M. Newnham

Quaternary environmental change in New Zealand: a review

The discovery that orbital variations are the driving force behind Quaternary climate change provides an impetus to set local and regional records of environmental change into the global context, a principle that has been strongly embraced by Quaternary scientists working in New Zealand. Their major achievements and significant current initiatives are reviewed here. The importance of the New Zealand Quaternary stems from its geographical context: a climatically sensitive, remote oceanic, southern location spanning 17 degrees of the mid-latitudes; an obliquely convergent plate boundary setting resulting in a high mountain range athwart the prevailing westerlies, active volcanism, a youthful and dynamic landscape, and mountains high enough to maintain glaciers today; and a remarkably short prehistory. The resultant records show marked environmental changes due not only to climatic oscillations but also to vigorous, active tectonism and volcanism. The Taupo Volcanic Zone, containing the worlds strongest concentration of youthful rhyolitic volcanoes, has produced at least 10 000 km3 of magma in the last 2 Ma. Climatic interpretations of records from marine sediments in the New Zealand region, together with several long sequences of alternating marine and terrestrial sediments, indicate broad synchrony with Northern Hemisphere events (within limitations of dating), although there are differences in detail for shorter-term climatic events. It is not yet certain that glacial advances coincided precisely with those in the Northern Hemisphere or were of similar duration. Late Cainozoic glaciation commenced c. 2.6-2.4 Ma but the record of glacial deposits is fragmentary and poorly dated except for the most recent events. The Last (Otira) Glaciation, from c. 100-10 ka, was characterized by at least five glacial advances including during the Last Glacial Maximum from 25 to 15 ka, when snowlines fell by 600-800 m. New Zealand evidence for cooling during the Younger Dryas stade is equivocal whilst isotopic records from speleothems, and other data, indicate warmer and wetter conditions from 10-7 ka, broadly conforming with records from mid-latitude Northern Hemisphere locations. Future advances will require sampling at shorter timescales, improvements in the accuracy and precision of existing dating methods and the development of new ones, extension of palaeoecological techniques to cover the full potential of new Zealands diverse biota, and a stronger emphasis on quantification of palaeoclimatic parameters.

Regional insolation forcing of late Quaternary climate change in the Southern Hemisphere

In agreement with the Milankovitch orbital forcing hypothesis it is often assumed that glacial–interglacial climate transitions occurred synchronously in the Northern and Southern hemispheres of the Earth. It is difficult to test this assumption, because of the paucity of long, continuous climate records from the Southern Hemisphere that have not been dated by tuning them to the presumed Northern Hemisphere signals. Here we present an independently dated terrestrial pollen record from a peat bog on South Island, New Zealand, to investigate global and local factors in Southern Hemisphere climate changes during the last two glacial–interglacial cycles. Our record largely corroborates the Milankovitch model of orbital forcing but also exhibits some differences: in particular, an earlier onset and longer duration of the Last Glacial Maximum. Our results suggest that Southern Hemisphere insolation may have been responsible for these differences in timing. Our findings question the validity of applying orbital tuning to Southern Hemisphere records and suggest an alternative mechanism to the bipolar seesaw for generating interhemispheric asynchrony in climate change.

A wiggle-match date for Polynesian settlement of New Zealand

Dating initial colonisation and environmental impacts by Polynesians in New Zealand is controversial. A key horizon is provided by the Kaharoa Tephra, deposited from an eruption of Mt Tarawera, because just underneath this layer are the first signs of forest clearance which imply human settlement. The authors used a log of celery pine from within Kaharoa deposits to derive a new precise date for the eruption via “wiggle-matching” – matching the radiocarbon dates of a sequence of samples from the log with the Southern Hemisphere calibration curve. The date obtained was 1314 ± 12 AD (2σ error), and the first environmental impacts and human occupation are argued to have occurred in the previous 50 years, i.e. in the late 13th – early 14th centuries AD. This date is contemporary with earliest settlement dates determined from archaeological sites in the New Zealand archipelago

Holocene vegetation, climate and history of a raised bog complex, northern New Zealand based on palynology, plant macrofossils and tephrochronology

A Holocene history of vegetation, climate, and ombrogenous mire development is presented from pollen and plant macrofossil analyses of sediments at Kopouatai Bog, a large, raised, restiad bog in northern New Zealand. Tephra layers of established ages, supplemented by numerous radiocarbon dates, provide a secure chronology. The earliest peats, overlying last glacial sediments, and dated at c. 11700 radiocarbon years BP, with extensive accumulation after c. 10360 BP, are dominated by pollen of warm temperate podocarp-angiosperm forest, indicating a moist, mild early-Holocene climate. The bog began as a series of small soligenous mires within lowland podocarp-dominated swamp forest but was mostly oligotrophic by c. 8500 BP. Peat accumulation rates have varied spatially and temporally, averaging 0.9 mm yr-1 in central and southern areas. The deposition of deltaic muds in the northern part of the bog accompanied a marine transgression c. 6500-5000 BP, while elsewhere an associated groundwater table rise resulted in a temporary return to mesotrophic conditions. As the marine influence subsequently receded, the northern areas remained subject to regular flooding, but underwent rapid peat growth at a mean rate of 1.7 mm yr-1, while oligotrophic conditions returned to other parts of the bog. Regional vegetation developments indicate a change, c. 6000 BP, to drier, frostier conditions during the late Holocene. Ascarina lucida and Agathis australis may be used as regional pollen- stratigraphic markers for the early Holocene and late Holocene, respectively. The loss of tall trees and expansion of subcanopy species and seral vegetation in forests near Kopouatai Bog, just before the deposition of Kaharoa Tephra (c. 700 BP), are likely evidence for human activity dating from at least this time.

Tourism and sustainable water supply in Mallorca: a geographical analysis

Abstract Problems of sustainability of water supply in tourist resorts are becoming an increasingly common and important issue in applied geography and environmental management. This paper examines the relationships between tourism and water supply on the Mediterranean island of Mallorca, discussing both the scale of the problem and recent measures to find a solution, particularly the proposed Hydrological Plan for the Balearic Islands (published in 1998/9). Since Mallorca lies in an area likely to be seriously affected by future climate change, its potential effects are discussed and evaluated. One of the most critical problems relates to the coarse spatial resolution of general circulation models for predicting precipitation in an area where precipitation regimes grade steeply from semi-arid to humid temperate. However, it is likely that a continuation of the marked inter-annual and decadal-scale variability in precipitation seen during the recent past probably poses a greater threat to Mallorca’s water supply than the more gradual, progressive change typically predicted to accompany future global warming. Similarly, continued over-exploitation of coastal aquifers will be more critical to water quality issues than the direct impacts of any future sea level rise, although the latter would undoubtedly exacerbate these effects. The conclusion discusses the controversial new ecotasa (‘ecotax’), due to be imposed on Mallorca’s tourist industry in 2002, which is likely to represent only a partial solution to the long-term water supply problem. As the physical, cultural and economic environments of Mallorca are typical of much of the Mediterranean region, the implications of this issue extend well beyond the island’s shores.

Fine-resolution pollen record of late-glacial climate reversal from New Zealand

The temporal relationship between rapid climate shifts in the Northern and Southern Hemispheres at the end of the last glacial is crucial to understanding how the global climate system functions during periods of major transition. A detailed Southern Hemisphere mid-latitude pollen record from a climatically sensitive and well-dated upland site in New Zealand, unlike previous interpretations, shows clear evidence of late-glacial climate changes similar in structure to those in the Northern Hemisphere, including a cooling interval from ca. 11 600 to 10 700 14 C yr B.P. Because the cooling interval occurred ca. 600 14 C yr before the Younger Dryas chron, our record thus also suggests that some global climatic events during the last deglaciation may have registered earlier in the Southern Hemisphere.

Stratigraphy and chronology of a 15 ka sequence of multi‐sourced silicic tephras in a montane peat bog, eastern North Island, New Zealand

We document the stratigraphy, composition, and chronology of a succession of 16 distal, silicic tephra layers interbedded with lateglacial and Holocene peats and muds up to c. 15 000 radiocarbon years (c. 18 000 calendar years) Did at a montane site (Kaipo Bog) in eastern North Island, New Zealand. Aged from 665 ± 15 to 14 700 ± 95 I4C yr BP, the tephras are derived from six volcanic centres in North Island, three of which are rhyolitic (Okataina, Taupo, Maroa), one peralkaline (Tuhua), and two andesitic (Tongariro, Egmont). Correlations are based on multiple criteria: field properties and stratigraphic interrelationships, ferro- magnesian silicate mineral assemblages, glass-shard major dement composition (from electron microprobe analysis), and radiocarbon dating. We extend the known distribution of tephras in eastern North Island and provide compositional data that add to their potential usefulness as isochronous markers. The chronostratigraphic framework established for the Kaipo sequence, based on both site-specific and independently derived tephra-based radiocarbon ages, provides the basis for fine-resolution paleoenvironmental studies at a climatically sensitive terrestrial site from the mid latitudes of the Southern Hemisphere. Tephras identified as especially useful paleoenvironmental markers include Rerewhakaaitu and Waiohau (lateglacial), Konini (late- glacial-early Holocene), Tuhua (middle Holocene), and Taupo and Kaharoa (late Holocene).

Rapid sea-level rise in the Gulf of Maine, USA, since AD 1800

Two sea-level records from salt marshes in coastal Maine are derived from foraminiferal analyses and AMS 14C, 210Pb, 137Cs and pollen chronology. Both records cover the period from AD 800 until the present and show corresponding patterns of sea-level change when corrected for trends which could accommodate millennial-scale isostatic adjustments. The records provide a detailed sea-level chronology for the last few centuries and thus link the instrumental (tide-gauge) record with the long-term geological record of sea-level change. Results show that sea level was relatively stable between AD 800 and 1300 and reached a lowstand around AD 1800, which was preceded by an oscillation in the eighteenth century. Since AD 1800, sea levels in the Gulf of Maine have risen by 0.3-0.4 m. The onset of this rise corresponds with regional climatic warming and could be interpreted as thermal expansion of the Gulf of Maine and North Atlantic sea surface. Sea-level rise possibly slowed temporarily during the mid-nineteenth century, but twentieth-century rates are unprecedented in the last millennium and correspond with hemispheric warming.

Studies of vegetation burial: a focus for biogeography and biogeomorphology?

This paper examines the literature on research into the effects of burial by deposition of blown sand, volcanic deposits (tephra, lavas and lahars) or fluvial sediment on vegetation and the subsequent capacity of the vegetation for survival and regeneration. Research on this topic involves the understanding and skills of the biogeographer, the ecologist and the geomorpholo-gist and represents a potentially very interesting area for integration between these areas of physical geography. Burial is closely linked to concepts of plant succession and pedogenesis. A general model of burial stress is presented that shows how types of stress are linked to the burial environment and the characteristics of the burial event, in particular the magnitude and frequency. The importance of elasticity of response of species to burial is vital, as demonstrated by the evolution of certain species, such as those of the genus Ammophila in sand dunes that appear to respond positively to the burial process. Research into burial by dust deposition, by volcanic tephra and lavas, by sand in coastal and lake dune environments, in desert environments and by alluvium and ‘run-on’ following hydro-logical events are reviewed in turn. The significance of burial to palaeoenvironmental and palaeoecological research is then demonstrated by reference to machair sand dune stratification in the Outer Hebrides and vegetation damage and burial following proximal volcanic impacts in New Zealand. Finally, methods of experimental research into burial in both the field and in the greenhouse are summarized and the conclusion stresses the need for more holistic approaches to the study of burial that link the biogeographical aspects of plant ecophysiology and both individual species and community ecology to the various geomorphic processes of deposition and sedimentation.

Environmental change during the last glacial maximum (c. 25 000-c. 16 500 years BP) at Mt Richmond, Auckland Isthmus, New Zealand

Abstract A 2 m section at the base of Mt Richmond contains a palynological record of the last glacial maximum (LGM) (c. 25 000‐c. 16 500 14C years BP) vegetation of the Auckland Isthmus. Three silicic tephra layers derived from the Taupo Volcanic Centre (Okaia Tephra c. 23 500 14C years BP, Kawakawa Tephra c. 22 500 14C years BP) and the Okataina Volcanic Centre (Okareka Tephra c. 18 000 14C years BP), both centres lying within the Taupo Volcanic Zone, provide the basis of the chronology supported by radiocarbon dates. The pollen diagram is divided into two pollen zones separated by the deposition of a locally derived basaltic ash. From c. 25 000–23 000 14C years BP the site was initially a eutrophic lake fringed by Leptospermum and Typha, which altered to a Cyperaceae/Leptospermum‐dominated swamp. The regional vegetation at the time was beech‐dominated forest; canopy conifers were present but formed a minor part of the local forest. From c. 23 000–16 500 14C years BP regional forest was further restricted to local patches in extensive shrubland/grassland. Temperatures may have been depressed by more than 4–5°C. The eruption of a local volcano dammed the swamp outlet resulting in a return to lacustrine conditions. Local volcanism may have accelerated vegetation change already under way as a result of climate change to cooler conditions. This record provides a view of LGM vegetation of the Auckland Isthmus and a template for earlier cold stages of the Quaternary.