Krista M McKinzey

Institute of Geography, School of GeoSciences, The University of Edinburgh Drummond Street, Edinburgh EH8 9XP Scotland, UK

Drummond Street Edinburgh Scotland

The Franz Josef Glacier (FJG) descends from the western peaks of the Southern Alps of New Zealand (Fig. 54.1A). It is one of the world's lowest lying mid-latitude glaciers and as of March 2001 terminated at 275ma.s.l. This maritime valley glacier has a terminus response time of 5-20yr (Oerlemans, 1997), which implies that it responds rapidly to perturbations in temperature, precipitation and, hence, mass balance.

Recently, the Little Ice Age (LIA) history of the FJG was reassessed using mapped tree-ring counts and diameter at breast height (DBH; 1.4m) measurements of the largest southern rata (Metrosideros umbellata) and kamahi (Weinmannia racemosa) within moraine limits and trimlines to determine the minimum time elapsed since deglaciation (McKinzey, 2001). This approach differed from previous interpretations because it used rata as the critical indicator species for the time elapsed since deglaciation (rather than kamahi alone, which consistently underestimates the timing of surface exposure) and combined both tree size and age for the reconstruction. Accordingly, the FJG's LIA maximum culminated before ad 1600 (rata > 225 cm DBH; Fig. 54.1B & C), when it terminated 4.5km down-valley of its 2001 position. Subsequent, but smaller magnitude, readvances occurred by ca. ad 1600 (3.7km down-valley, rata and kamahi 100-200cm DBH) and ca. ad 1800 (3.2km down-valley, rata and kamahi <60cm DBH). Numerical modelling experiments have delimited possible climatic envelopes for equilibrium lengths of the FJG during the LIA. Results indicate a minimum cooling of -1.15°C or +57% precipitation for the LIA maximum extent (departures relative to 1970-1999 mean temperature and precipitation), —1°C or +47% precipitation for the second LIA advance and —0.8°C or +37% precipitation for the third LIA advance (Anderson, 2004).

Other proxy evidence of late Holocene climate change in New Zealand corroborates an early LIA maximum for the FJG.

The speleothem record from northwest Nelson indicates periods of prolonged cold temperatures ca. ad 1400-1450 and ca. ad 1600-1650 (Wilson et al., 1979). Additionally, tree-rings from silver pine (Lagarostrobos colensoi) growing at Oroko Swamp reveal that the coldest time in New Zealand during the LIA occurred during the early 16th century when temperatures declined by ca. —1.5°C (Cook et al., 2002). Subsequent cold periods of smaller magnitude occurred around the early 17th and late 18th centuries. Strengthened southwesterly airflow during the LIA (see Schulmeister et al., 2004), which would have brought an influx of cool, moisture-laden air across the Southern Alps, possibly triggered sudden switches in the FJG's mass balance, manifested as a series of rapid fluctuations of the glacier terminus.

Regionally, some glaciers of the Southern Alps reached their LIA maxima at least a century earlier (14th-16th centuries; Fig. 54.2) than the 'classic' period of maximum LIA glacier advances (17th-19th centuries) across large parts of the Northern Hemisphere. Furthermore, glaciers in the North Atlantic were still advancing towards their maxima when New Zealand glaciers, including the FJG, experienced their final and smallest magnitude LIA advance. This suggests that climatic amelioration occurred in New Zealand by the early 19th century. Overall, the New Zealand glacial record presents increasing evidence that both the timing and magnitude of LIA climate change and glacier response between hemispheres were not necessarily synchronous.

Historical records in New Zealand date from ca. ad 1860, and numerous accounts document glacier readvances throughout the late 19th century, although glaciers never regained their volume lost since the end of the LIA. Somewhat periodic, short-term advances of the FJG superimposed on long-term recession during the 20th century suggest complicated relationships between glacier behaviour, climate and synoptic-scale circulation (e.g.

Auckland

New Zealand

NW Nelson

Wellington

Southern Alps

Oroko Swamp Arrowsmith Range

„, FJG Christchurch

Fox Glacier

South Island

LIA 1

1750 Sign

250 500 750 1000 Meters

0 250 500 750 1000 Meters

250 500 750 1000 Meters

LEGEND

Moraine

(174) Largest measured rata or kamahi (DBH in cm) per quadrat 1856(37) Oldest dated kamahi core per quadrat (DBH in cm)

X1780 (36R) Oldest rata (R) or kamahi (K) cross-section (DBH in cm)

1749 134 K)

Q235)) Data used to estimate extent/magnitude of LIA glacier expansion

Figure 54.1 (A) The FJG, New Zealand (43°26'S, 170°10'E), and other key South Island locations referred to in text. (B) The reconstructed LIA chronology of the FJG, including prominent trimlines on the eastern valley side, and the first historically dated position of the ice-front as photographed by T. Pringle in ad 1867. Surface contours are drawn every 200m. (C) Enlargement of the valley floor area with data illustrated as in (B). Previous interpretations of the LIA maximum extent have also been drawn, e.g. the ad 1750 sign (cf. Lawrence & Lawrence, 1965), PW (Wardle, 1973) and CB (Burrows, 1990). (After McKinzey, 2001.)

Figure 54.2 Comparison of LIA records for selected glaciers of the Southern Alps. The Fox Glacier chronology (cf. Wardle, 1973) is derived mainly from tree-ring counts including kamahi (but not rata). Discrepancies regarding the timing of the LIA maximum at the Mueller Glacier may, in part, be reconciled by independent radiocarbon dates from the nearby Tasman Glacier (Burrows, 1989, personal communication), which support an early 15th century maximum extent. However, along with the reassessed FJG chronology, these examples highlight the necessity of further research across the region. (After McKinzey, 2001.)

Figure 54.2 Comparison of LIA records for selected glaciers of the Southern Alps. The Fox Glacier chronology (cf. Wardle, 1973) is derived mainly from tree-ring counts including kamahi (but not rata). Discrepancies regarding the timing of the LIA maximum at the Mueller Glacier may, in part, be reconciled by independent radiocarbon dates from the nearby Tasman Glacier (Burrows, 1989, personal communication), which support an early 15th century maximum extent. However, along with the reassessed FJG chronology, these examples highlight the necessity of further research across the region. (After McKinzey, 2001.)

Hooker & Fitzharris, 1999). Thus, the reassessed LIA history of the FJG can be used as a key resource with which to refine future predictions about glacier-climate interactions. Moreover, additional multiparameter dating studies are required to further elucidate the Southern Alps glacial record, especially for those climatically sensitive, such as the FJG, so that the nature of interhemispheric connections for recent events, such as the LIA, can be better understood.

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