Environmental Change in Tropical Terrestrial Environments:
New Guinea Highlands and Lowlands
Prentice, M. L.¹, Hope, G. S.², Maryunani, K.³, Schimmelmann, A.♣, Sauer, P.♣.
¹ Geoscy, LLC, Bloomington IN, ² Australian National University, Canberra, Australia, ³ Institute of Technology at Bandung, Bandung Indonesia ♣ Department of Geological Sciences, Indiana University, Bloomington IN
New Guinea is the worlds largest and highest tropical island with environments that span altitudes from sea level to 4,800 m above sea level (Fig. 1). Geoscy is a partner in studies of environmental change in both the highlands and lowlands of New Guinea. Geoscy’s role is evaluation of environmental change using sedimentary geology-geomorphology. In the highlands, Geoscy investigates records of past glacier change, lake and swamp change, river change, karst development, and mountain erosion. This work complements that of Geoscy collaborators who focus on changes in vegetation and peat including their chemistry. In the lowlands, Geoscy investigates a variety of geologic records of coastline change.
Fig. 1. Physiographic map of New Guinea and surrounding islands showing topography and rivers. The highlands are terrain above 1500 m altitude.
The New Guinea landscape is highly dynamic because of rapidly expanding development, highly variable weather and climate, and active tectonic forces. The island is located adjacent to the warmest part of the global ocean which drives the largest atmospheric convection system on the planet. This ocean-atmosphere system is quite variable over periods of several years resulting in significant swings in island climate. As a major flywheel in the global-scale El Nino-Southern Oscillation cycle, variations in the ocean-atmosphere system north of New Guinea initiate major variations in global inter-annual weather patterns.
Politically, New Guinea is divided midway between Papua New Guinea on the east and Indonesia on the west (Fig. 2). Geoscy works in both countries. The overall program has implications for resource availability and sensitivity, habitat stability, and climate change, all of which impact agriculture, biodiversity, and the economy of both countries.
Fig. 2. Political map of New Guinea showing international and provincial boundaries and some major cities. The western half of the island is part of Indonesia. The eastern half is of part Papua New Guinea.
Glaciers and mountain ice caps were extensive in the New Guinea highlands above 3000 m during the last glacial cycle. The last remnants of these glaciers have held on next to Mt. Jayawijaya in western New Guinea until the last few years (Figs. 3). As a result of a long history, glacial deposits form a major component of highland environments across the 2,000 km long spine of New Guinea. These deposits provide the most direct evidence of past climate change in the highlands, a major chapter of New Guinea natural history, and potentially contain significant mineral resources.
Fig. 3. Generalized topography of New Guinea. Lowland terrain dominates north and south of the central range which is laregly above 2500 m and reaches a high of 5000 m at Mt. Jayawijaya.
The shrinkage of glaciers over the last 200 years adjacent to Mt Jayawijaya (Carstensz Pyramid) is mapped in Fig 4. Because these glaciers erode and deposit sediment at a high rate, this map in effect shows the extent and approximate ages of glacial deposits of the last 200 years. The deposits provide the most direct evidence for significant, long-term warming in the New Guinea highlands and indeed over the western tropical Pacific Ocean. Instrumental weather records in the highlands are sparse and at most a few decades long.
Fig. 4. The extent of glaciers and glacial deposits of the last few hundred years on the Mt Jayawijaya massif. See Fig. 3 for location.
Fig. 5. Aerial view of glaciers and ice fields on the Mt. Jayawijaya massif in 1972. This picture corresponds to the pink deposits and time slice in Fig. 4.
Glacial deposits cover much of New Guinea terrain above 3600 m including the Kemabu Plateau which is adjacent to Mt Jayawijaya (Fig. 6). The total area of glacial terrain across New Guinea* is about the same as the size of the State of Rhode Island. However, New Guinea deposits appear to be 10s to 100s of meters thick and probably contain economic minerals given the mineral resources already mined across the Central Range of the island.
Fig. 6. The maximum extent of glacial deposits (gray area) on the Kemabu Plateau and Pk. Jayawijaya sector of the Central Range. Inset map show the location of the Kemabu Plateau in western New Guinea.
* Prentice, M. L., Hope, G. S., Peterson, J. A., and Barrows, T. T., 2011, The glaciation of the south-east Asian equatorial region, in Ehlers, J. J., Gibbard, P. L., and Hughes, P. D., eds., Quaternary Glaciations- Extent and Chronology- A Closer Look: Amsterdam, Elsevier, p. 1023-1036.
In the New Guinea lowlands, Geoscy is working on ocean sediment cores collected from Cenderawasih Bay, a large inland sea on the northwest coast, along a transect that is oriented to target the Derewo River delta (Fig. 7). The Derewo River drains a large watershed encompassing a tremendous elevation range because it includes the strongly glaciated terrain of the Mt. Jayawijaya massif up to 4800 m above sea level. These cores provide long-term historical perspective on many aspects of environmental change. Environmental problems that we are addressing include the history of sediment and water flux from the Derewo River, erosion of the northern flank of the New Guinea Central Range, oceanographic conditions such as temperature, salinity, and circulation in the bay, watershed vegetation and climate, and, lastly, sea level, shoreline position, and land area.
We focus on sediment core MD012382 that was raised from a depth of 395 m on the front of the Derewo River delta, about 50 km from the shoreline (Fig. 8). This core is 34 m long.
Fig. 7. Map of Cenderawasih Bay that shows the locations of the three cores in our study (red triangles). Core MD012382 is closest to the mouth of the Derewo River. Color scheme over land represents topography with white representing terrain above 2500 m elevation. The upper Derewo watershed includes the formerly glaciated terrain shown in Fig. 6.
Fig. 8. Bathymetric map of the area around core MD012382 on the front of the Derewo River delta. Colored circles with numbers are water depths.
The Cenderawasih Bay cores were collected during Leg 1 of the WEPAMA cruise MD 122/IMAGES VII that used the French RV Marion Dufresne (Figs. 9, 10)*.
Fig. 9. The 120 m long RV Marion Dufresne at dock in Kupang, Indonesia. The French supply/logistics/research vessel has a unique, unobstructed starboard main deck that allows deployment and recovery of a giant ‘Calypso’ piston-corer.
Fig. 10. Deployment of the giant Calypso piston-corer off the starboard main deck of the RV Marion Dufresne. The top of the vertical core barrel loaded with lead weights (orange) is visible in the picture.
One of our primary objectives is to determine the age of different levels in the core by radiocarbon dating. An age model for the core is essential to determining the history of sediment accumulation at the site and dating the environmental indices measured using core components. We measured the radiocarbon age of several woody and carbonate samples and produced a preliminary age model (Fig 10). Based on these radiocarbon ages, we estimate that the base of the core dates to 16,000 years ago. Additionally, the radiocarbon dates suggest that sedimentation rates increased to very high rates starting about 2000 yrs ago from what is considered a high average sedimentation rate over the preceding 10,000 yrs (Fig.11).
Fig. 11. Preliminary age depth curve (black line) and radiocarbon dates for MD012382. Wood fragment dates are in red. Carbonate dates are in blue. Average sedimentation rates for three core intervals are shown in cm/decade.
** Bassinot, F., Baltzer, A., Chen, M.-T., DeDeckker, P., Khunt, W., Levitan, M., Nurnberg, D., Oba, T., Prentice, M. L., Sarnthein, M., Situmorang, M., and Tiedemann, R., 2002, WEPAMA Cruise MD 122/IMAGES VII, Plouzane, France, Institut Polaire Francais, Les rapports des campagnes a la mer, 453 p.