The Caribbean plate converges obliquely at ~2 cm/yr toward the North American plate (Figure 1). T... more The Caribbean plate converges obliquely at ~2 cm/yr toward the North American plate (Figure 1). This transpression is partly accommodated across the island of Hispaniola by the partitioning of motion between a fold-and-thrust belt trending NW-SE, and two E-W left-lateral fault systems. The southern fault, the Enriquillo-Plantain Garden Fault (EPGF), is morphologically well expressed in western Haiti but its precise geometry in eastern Haiti is debatable. There, Lake Azuei stretches over 20 km in a direction parallel to the fold-and-thrust belt while its southern shoreline strikes EW, parallel to the expected trend of the EPGF. We acquired 220 km of multichannel seismic reflection (MCS) profiles across its surface. This dataset documents the following structures: 1) The western side of the lake is occupied by a broad NW-trending monoclinal fold (Figures 2 & 3). We propose that this monocline is the surface expression of a SW-dipping, NW-striking blind thrust fault. The progressive steepening of the seismic horizons with depth (Figures 2, 3, and 5) suggests that it has been continuously active during the deposition of at least 300 m of sediments. 2) A ~2 km-wide deformation zone borders the EW-trending southern shore (see map poster T31D-0268, at left). This deformation zone is faintly imaged below a shallow gas front (Figure 4). We propose that it corresponds to a series of faultpropagation folds that develop ahead of an EW, S-dipping oblique-slip fault. This interpretation is compatible CHIRP profiles acquired concurrently with our MCS data and that document folding of the topmost turbidites but a lack of evidence for any stratigraphic offset across faults (see poster T31D-0268, at left). 3) A NW-trending fold imaged between the monoclinic fold to the west and the Matheux Mountain to the east indicates that ongoing tectonic deformation affects the entire length and width of the lake (Figure 6).
The North American-Caribbean plate boundary cuts EW across the island of Hispaniola (Figure 1, to... more The North American-Caribbean plate boundary cuts EW across the island of Hispaniola (Figure 1, top). RelaYve moYon is transpressional and, overall, deformaYon is parYYoned between a NW-SE fold-andthrust belt and two E-W le^-lateral faults 150 km apart. The southern fault, the Enriquillo-Plantain Garden Fault (EPGF), is well defined in western HaiY but poorly defined as it nears Lake Azuei in eastern HaiY (Figure 1). Holocene deformaYon is well recorded in Lake Azuei upper straYgraphy and lakebed morphology. We analyzed 200 km of subboJom (CHIRP) profiles collected in 2017 that imaged the upper 2-10 m of sediments (Figure 2); this dataset is complemented 140 km of echosounder profiles (MoknaYan et al., 2017) and 65 km of CHIRP profiles (Wang et al., 2018). Morphological and straYgraphic informaYon extracted from the combined dataset is compiled into a detailed geological map (Figure 3). This compilaYon reveals: 1. Gas-charged sediments occur across most of the flat lake floor. However, where the gas front is deeper, the CHIRP data show the rhythmic straYgraphy characterisYc of turbidites.. 2. Turbidite beds fold up along the edges of the lake floor, documenYng the ongoing deformaYon of the basin margins (Figures 3-2, 3-3, 3-4) 3. Deeper penetraYon seismic reflecYon profiles reveal a NW-trending monoclinic fold in the western part of the lake (see poster T31D-0269 at right). The front of the monocline is segmented, and possibly offset by one or more tear faults. 4. In the southern part of the lake, a right-stepping en echelon folds trend EW. This geometry is compaYble with fault-propagaYon folds developing ahead of a S-dipping oblique-slip fault which may be associated with the EPGF (Figures 3-5, 3-6). We suggest that this deformaYon is due principally to the compressional rather than the shear component of transpression. 5. We find no evidence of fault scarp or straYgraphic offset in that same area, as might be expected from a sub-verYcal EPGF (Figure 3-6). 6. So^ sediment deformaYon occur on the surface of the monocline (Figure 3-9). These probable liquefacYon features are located next to a < 2 kyr-old, 11 m-deep paleoshoreline which is upli^ed 1 to 2 meters (Cormier et al., 2018) (Figures 3-3,3-4, 3-5, 3-6). A large earthquake on a presumed SW dipping blind thrust fault underlying the monoclinic fold could explain both these features. If this interpretaYon is correct, it suggests that this structure is seismically hazardous. 7. A fan delta is prograding into the southern basin, overprinYng the possible trace of the EPGF (Figure 3-7). Figure 3: Geological features interpreted from CHIRP and mulYchannel seismic reflecYon profiles.
Lake Towuti (2.5°S, 121.5°E) is a longlived, tectonic lake located on the Island of Sulawesi, Ind... more Lake Towuti (2.5°S, 121.5°E) is a longlived, tectonic lake located on the Island of Sulawesi, Indonesia, and in the center of the Indo-Pacific warm pool (IPWP). Lake Towuti is connected with upstream lakes Matano and Mahalona through the Mahalona River, which constitutes the largest inlet to the lake. The Mahalona River Delta is prograding into Lake Towuti's deep northern basin thus exerting significant control on depositional processes in the basin. We combine high-resolution seismic reflection and sedimentological datasets from a 19.8-m-long sediment piston core from the distal edge of this delta to characterize fluctuations in deltaic sedimentation during the past *29 kyr BP and their relation to climatic change. Our datasets reveal that, in the present, sedimentation is strongly influenced by deposition of laterally transported sediments sourced from the Mahalona River Delta. Variations in the amount of laterally transported sediments, as expressed by coarse fraction amounts in pelagic muds and turbidite recurrence rates and cumulative thicknesses, are primarily a function of lake-level induced delta slope instability and delta progradation into the basin. We infer lowest lake-levels between *29 and 16, a gradual lake level rise between *16 and 11, and high lake-levels between *11 and 0 kyr BP. Periods of highest turbidite deposition, *26 to 24 and *18 to Electronic supplementary material The online version of this article (
The tropical Pacific plays a fundamentally important role in global climate change due to the int... more The tropical Pacific plays a fundamentally important role in global climate change due to the interaction between the El Niño Southern Oscillation (ENSO), the Intertropical Convergence Zone (ITCZ), and the Asian monsoons. Indonesia sits at the heart of the tropical western Pacific, yet we have very few terrestrial paleoclimate records from Indonesia to evaluate hydrological changes in the tropical western
Proceedings of the National Academy of Sciences, 2014
Significance Climate variability in the tropical western Pacific exerts enormous influence on glo... more Significance Climate variability in the tropical western Pacific exerts enormous influence on global climate, yet its history remains poorly constrained. We present the region’s first continuous terrestrial sedimentary record of surface hydrology and vegetation spanning the last 60,000 y based upon geochemical data from Lake Towuti, Indonesia. Our data demonstrate that wet conditions and rainforest ecosystems present during the Holocene and during marine isotope stage 3 were interrupted by severe drying between ∼33,000 and 16,000 y B.P., when high-latitude ice sheets expanded and global temperatures cooled. These findings indicate an important role for glacial boundary conditions in pacing tropical western Pacific climate change, and highlight the potential for the western Pacific to amplify global climate change during glacial–interglacial cycles.
ABSTRACT Indonesia sits at the western edge of the tropical Pacific warm pool, and its climate re... more ABSTRACT Indonesia sits at the western edge of the tropical Pacific warm pool, and its climate responds to the Australasian monsoon and the intertropical convergence zone (ITCZ). Despite Indonesia&#39;s climatological significance, we have very few records of the region&#39;s hydrology. To fill this gap, in 2010 we collected long sediment piston cores and seismic reflection data from Lake Towuti, Sulawesi (2.5 S, 121 E), the largest lake in Indonesia. We are building new reconstructions of regional hydrology based upon sedimentological, geochemical, magnetic, core-scanning x-ray fluorescence, and compound-specific stable isotopic data to develop the first continuous record of rainfall and drought over the last 60,000 years from the maritime continent. Our record shows that, at the orbital scale, the boreal winter monsoon-dominated climate of central Indonesia responds to both precessional forcing of the Australasian monsoon and high latitude glacial processes. We observe relatively dry conditions at 60 kyr BP, wet conditions during much of Marine Isotope Stage 3 (MIS3), and a dry early/wet late Holocene. This is antiphased with speleothem 18O/16O records from China (e.g. Wang et al., 2008, Nature 451: 1090-1093), and is consistent with southward migration of the ITCZ over Indonesia and Australia during precession maxima. However, we observe the driest conditions of the last 60 kyr during the last glacial maximum (LGM), when southern hemisphere summer insolation was low. Previous studies (e.g. Griffiths et al., 2009, Nature Geosciences 2: 636-639) have suggested that exposure of the Sunda Shelf during the LGM reduces central Indonesian convection. However, we observe little effect of Sunda Shelf exposure on Indonesian hydrology during MIS3, and the deglacial rise in precipitation appears rapid in our data relative to sea level rise. We suggest that cool sea surface temperatures in the maritime continent, driven by greenhouse gas minima and associated glacial processes, reduced LGM convection over Indonesia. We observe substantial millennial-scale variability during MIS3 as well as the last glacial termination. For instance, Heinrich event 1 is a prominent arid event, as is the Younger Dryas. Aridity in central Indonesia during these North Atlantic stadials indicates that the &quot;northern mode&quot; of millennial climate variability observed in mainland Asia propagates south of the equator over maritime Indonesia, despite clear evidence for southward migration of the ITCZ. This suggests that water vapor content and convection within the ITCZ controls central Indonesian hydrology more than ITCZ position.
More than 100 km of seismic reflection profiles together with a new multibeam survey of the sedim... more More than 100 km of seismic reflection profiles together with a new multibeam survey of the sediment fill in lake Hestvatn, South Iceland, reveal two sub-basins filled with up to 44 m of deglacial and Holocene sediment. The chronology is constrained by geochemically characterized tephra layers and radiocarbon dates on marine molluscs. The Vedde Ash and Saksunarvatn Ash provide key chronological control for the deglacial sediment. Five seismic units are tied to the lithostratigraphy of sediment cores obtained from the two basins. The seismic units reveal major changes from glacial, to glacial-marine, to lacustrine sedimentary environments. Isopach maps of the seismic units document changes in the primary sediment depocenters, sedimentation rates and sediment delivery through time. The Vedde Ash, found only in glacial-marine sediment in the southern basin, suggests that during the Younger Dryas the northern basin of Hestvatn was occupied by an outlet glacier from the main Icelandic Ice Sheet that calved into a marine embayment. A high-resolution multibeam bathymetric survey reveals multiple shallow ridges between the two sub-basins of Hestvatn, which presumably acted as a pinning point for the calving glacier. During and after the retreat of the glacier and isolation of the lake basin, lacustrine sediments were mainly deposited via northern and northwesterly inlets, resulting in higher sedimentation rates in the north basin compared to the south basin. Early in the lacustrine phase repeated turbidites were deposited, interpreted to originate in glacial outburst floods (jökulhlaups) following a retreating ice-margin in central Iceland.
Glaciers often terminate in lakes, where they may form prominent moraines, and are considered rel... more Glaciers often terminate in lakes, where they may form prominent moraines, and are considered relatively stable. During the Little Ice Age (LIA: ca 1300-1900AD), strong regional cooling across the northern North Atlantic led to widespread glacier advances. At its peak, summer temperatures in Iceland are estimated to have been 3 to 4 °C lower than during the early Holocene optimum
Efforts to restore self-sustaining lake trout (Salvelinus namaycush) populations in the Laurentia... more Efforts to restore self-sustaining lake trout (Salvelinus namaycush) populations in the Laurentian Great Lakes have had widespread success in Lake Superior; but in other Great Lakes, populations of lake trout are maintained by stocking. Recruitment bottlenecks may be present at a number of stages of the reproduction process. To study eggs and fry, it is necessary to identify spawning locations,
The tropical western Pacific Ocean exerts a dominant influence on the Earth's atmospheric hea... more The tropical western Pacific Ocean exerts a dominant influence on the Earth's atmospheric heat and moisture budgets. Continental drilling of lake deposits through DOSECC and ICDP has begun to provide critical new information on the Plio-Pleistocene history of tropical continental climate, yet no potential drilling sites have been identified in the tropical western Pacific. Here we report results from the first seismic reflection studies ever conducted on large lakes in Indonesia that highlight the potential of Lake Towuti, South Sulawesi, for obtaining long terrestrial records of western Pacific climate. We have collected nearly 500 km of high-resolution seismic reflection (CHIRP) data from Lakes Matano (164 km2, 590 m deep) and Towuti (560 km2, 203 m deep), two of the Malili Lakes in central Sulawesi. These tectonic lakes formed about 2 Myr BP, and thus have the potential to provide long records of Indonesian climate. Seismic stratigraphic analyses of sediments from Lake Matano...
A series of airgun single-channel seismic-reflection profiles from Thunder Bay and the adjacent I... more A series of airgun single-channel seismic-reflection profiles from Thunder Bay and the adjacent Isle Royal Trough of Lake Superior suggest that water from Glacial Lake Agassiz did not catastrophically drain into Lake Superior at this locality, as has been previously suggested. Thunder Bay is underlain by a relatively smooth bedrock surface, the double bedrock sill at its mouth is not
ABSTRACT In the very fine-grained, gas-poor sediments of Lake Superior, it is possible to collect... more ABSTRACT In the very fine-grained, gas-poor sediments of Lake Superior, it is possible to collect extremely high resolution images of the subsurface with a 28 kHz echosounder. Penetration depths routinely exceed 20 m. This represents a significant portion of the lake&#39;s soft sediment section and makes it possible to image sediments that were deposited during the most recent de-glaciation of the basin. A high-resolution &quot;pseudo-3D&quot; seismic survey recently collected with this system in western Lake Superior provides convincing evidence of buried iceberg scouring in the lakefloor glaciolacustrine sediments. In seismic profiles, the scour appears as localized regions of acoustical blanking that are frequently &quot;U&quot; or &quot;V&quot;-shaped. The scour zones are typically 10s of meters across and up to 6 m deep. In plan-view, they exhibit a curvilinear appearance, frequently running for several kilometers. Many of the scour marks exhibit a WNW-ESE orientation, suggesting that the prevailing winds blew in this direction. Additional support for the iceberg-grounding interpretation is apparent from localized stratigraphic unconformities and raised lateral berms, interpreted to have been caused by iceberg- induced erosion and deformation of the ancient lake floor. By using the top of the scour marks as indicator of their relative age, it appears that the rate of calving into the lake changed over time, reaching a maximum shortly before the end of deposition of the red varved glaciolacustrine clays. Presumably this marks the final retreat of the Superior Lobe of the Laurentide Ice Sheet out of the lake. Earlier increases in scouring events, recorded in the sub-surface section are most likely the result of increases in calving during earlier minor readvances of the ice sheet.
ABSTRACT Glacial Lake Agassiz was the largest of the proglacial lakes to have formed in North Ame... more ABSTRACT Glacial Lake Agassiz was the largest of the proglacial lakes to have formed in North America during retreat of the Laurentide Ice Sheet. The extent of Lake Agassiz was controlled by a combination of factors including topography, ice position and amount of isostatic rebound. Many of the changes in the outlet location of the lake have been interpreted to involve a catastrophic release of water. Evidence for some of these catastrophic floods are visible in both terrestrial and sub-lacustrine records. An influx of freshwater from Lake Agassiz to the North Atlantic from such floods has been suggested as a possible trigger for the initiation of the Younger Dryas cold interval. A series of airgun single-channel seismic-reflection profiles from Thunder Bay and the adjacent Isle Royal trough of Lake Superior suggest that water from Glacial Lake Agassiz did not catastrophically release into Lake Superior at this locality, as has been previously suggested. Seismic surveys from a region further north within Lake Superior identified characteristic features of a later catastrophic release of water, which occurred after the Marquette glacial redadvance ca. 9,500 14C yr BP. The younger identified features to the north include bedrock scour and large debris fans, neither of which are present in the Thunder Bay area. Given the similarity in geomorphic conditions in the two locations, similar features are expected if the same type of catastrophic event occurred. Therefore, the absence of such features suggests that Lake Agassiz did not drain catastrophically through Thunder Bay. Instead of catastrophic outflow features in the seismic records, a thick package of distinct seismic units occur in the Isle Royale trough, which suggest a complex history of ice retreat and readvance. Trough parallel profiles show a massive seismic package, which grades into more individually distinguishable units in the direction of general ice retreat. These units appear to represent grounding-line fans deposited by Marquette ice during its retreat through the trough.
ABSTRACT Glacial Lake Agassiz was the largest of the North American glacial margin lakes. Over it... more ABSTRACT Glacial Lake Agassiz was the largest of the North American glacial margin lakes. Over its 4,000 year existence, Lake Agassiz varied substantially in aerial extent and volume. This variability was a function of the fluctuating retreat pattern of the Laurentide Ice Sheet&#39;s southwestern margin, differential isostatic rebound of the North American crust, the topography of the land exposed by the retreating ice, and erosion of the various outlet channels draining the lake. These factors combined to form a history of Lake Agassiz punctuated by sudden and sometimes catastrophic rerouting of its drainage from one outlet channel to another. The amount and routing of Lake Agassiz discharge has become controversial. However, extensive onshore observations of Glacial Lake Agassiz discharge features have firmly established that northwestern Lake Superior was a major drainage route following the retreat of the Marquette glacial advance ca. 9,500 years 14C BP. We describe a high-resolution single channel seismic reflection dataset collected with a small airgun that we acquired to test our hypothesis that this drainage event (corresponding to the Nipigon Phase of Lake Agassiz) left diagnostic stratigraphic and geomorphic signatures beneath Lake Superior. The unique bathymetry of northwestern Lake Superior, where water depth plunges off Nipigon and Black Bays, makes this location ideal for the identification and characterization of the Post-Marquette depositional features. The steep and sudden drop-off from the shallow water bays into the deep offshore waters of the lake would have caused the high-velocity floods to slow and drop much of the sediment they were carrying. Our results confirm the existence of these sediment packages, which are now buried below a thin blanket of Holocene sediment. They form wedges of sediment that are thickest (some over 70 m thick) in the deep water area adjacent to the flood outlet. The apron of sediment thins lakeward and shore-parallel away from the outlet. The seismic character of the basal units of the apron, proximal to the outlet, is chaotic and only very weakly stratified suggesting that these deposits represent coarse sediment laid down during the initial stages of the flood when flow was presumably at its peak. These sediments are overlain and draped by a weakly stratified package that is more widely developed (extending lakeward beyond the bounds of our survey). We interpret this unit, which becomes more stratified and thinner lakeward, to represent the fine grained sediment associated with the latter stages of the flood when flow had eased.
The Caribbean plate converges obliquely at ~2 cm/yr toward the North American plate (Figure 1). T... more The Caribbean plate converges obliquely at ~2 cm/yr toward the North American plate (Figure 1). This transpression is partly accommodated across the island of Hispaniola by the partitioning of motion between a fold-and-thrust belt trending NW-SE, and two E-W left-lateral fault systems. The southern fault, the Enriquillo-Plantain Garden Fault (EPGF), is morphologically well expressed in western Haiti but its precise geometry in eastern Haiti is debatable. There, Lake Azuei stretches over 20 km in a direction parallel to the fold-and-thrust belt while its southern shoreline strikes EW, parallel to the expected trend of the EPGF. We acquired 220 km of multichannel seismic reflection (MCS) profiles across its surface. This dataset documents the following structures: 1) The western side of the lake is occupied by a broad NW-trending monoclinal fold (Figures 2 & 3). We propose that this monocline is the surface expression of a SW-dipping, NW-striking blind thrust fault. The progressive steepening of the seismic horizons with depth (Figures 2, 3, and 5) suggests that it has been continuously active during the deposition of at least 300 m of sediments. 2) A ~2 km-wide deformation zone borders the EW-trending southern shore (see map poster T31D-0268, at left). This deformation zone is faintly imaged below a shallow gas front (Figure 4). We propose that it corresponds to a series of faultpropagation folds that develop ahead of an EW, S-dipping oblique-slip fault. This interpretation is compatible CHIRP profiles acquired concurrently with our MCS data and that document folding of the topmost turbidites but a lack of evidence for any stratigraphic offset across faults (see poster T31D-0268, at left). 3) A NW-trending fold imaged between the monoclinic fold to the west and the Matheux Mountain to the east indicates that ongoing tectonic deformation affects the entire length and width of the lake (Figure 6).
The North American-Caribbean plate boundary cuts EW across the island of Hispaniola (Figure 1, to... more The North American-Caribbean plate boundary cuts EW across the island of Hispaniola (Figure 1, top). RelaYve moYon is transpressional and, overall, deformaYon is parYYoned between a NW-SE fold-andthrust belt and two E-W le^-lateral faults 150 km apart. The southern fault, the Enriquillo-Plantain Garden Fault (EPGF), is well defined in western HaiY but poorly defined as it nears Lake Azuei in eastern HaiY (Figure 1). Holocene deformaYon is well recorded in Lake Azuei upper straYgraphy and lakebed morphology. We analyzed 200 km of subboJom (CHIRP) profiles collected in 2017 that imaged the upper 2-10 m of sediments (Figure 2); this dataset is complemented 140 km of echosounder profiles (MoknaYan et al., 2017) and 65 km of CHIRP profiles (Wang et al., 2018). Morphological and straYgraphic informaYon extracted from the combined dataset is compiled into a detailed geological map (Figure 3). This compilaYon reveals: 1. Gas-charged sediments occur across most of the flat lake floor. However, where the gas front is deeper, the CHIRP data show the rhythmic straYgraphy characterisYc of turbidites.. 2. Turbidite beds fold up along the edges of the lake floor, documenYng the ongoing deformaYon of the basin margins (Figures 3-2, 3-3, 3-4) 3. Deeper penetraYon seismic reflecYon profiles reveal a NW-trending monoclinic fold in the western part of the lake (see poster T31D-0269 at right). The front of the monocline is segmented, and possibly offset by one or more tear faults. 4. In the southern part of the lake, a right-stepping en echelon folds trend EW. This geometry is compaYble with fault-propagaYon folds developing ahead of a S-dipping oblique-slip fault which may be associated with the EPGF (Figures 3-5, 3-6). We suggest that this deformaYon is due principally to the compressional rather than the shear component of transpression. 5. We find no evidence of fault scarp or straYgraphic offset in that same area, as might be expected from a sub-verYcal EPGF (Figure 3-6). 6. So^ sediment deformaYon occur on the surface of the monocline (Figure 3-9). These probable liquefacYon features are located next to a < 2 kyr-old, 11 m-deep paleoshoreline which is upli^ed 1 to 2 meters (Cormier et al., 2018) (Figures 3-3,3-4, 3-5, 3-6). A large earthquake on a presumed SW dipping blind thrust fault underlying the monoclinic fold could explain both these features. If this interpretaYon is correct, it suggests that this structure is seismically hazardous. 7. A fan delta is prograding into the southern basin, overprinYng the possible trace of the EPGF (Figure 3-7). Figure 3: Geological features interpreted from CHIRP and mulYchannel seismic reflecYon profiles.
Lake Towuti (2.5°S, 121.5°E) is a longlived, tectonic lake located on the Island of Sulawesi, Ind... more Lake Towuti (2.5°S, 121.5°E) is a longlived, tectonic lake located on the Island of Sulawesi, Indonesia, and in the center of the Indo-Pacific warm pool (IPWP). Lake Towuti is connected with upstream lakes Matano and Mahalona through the Mahalona River, which constitutes the largest inlet to the lake. The Mahalona River Delta is prograding into Lake Towuti's deep northern basin thus exerting significant control on depositional processes in the basin. We combine high-resolution seismic reflection and sedimentological datasets from a 19.8-m-long sediment piston core from the distal edge of this delta to characterize fluctuations in deltaic sedimentation during the past *29 kyr BP and their relation to climatic change. Our datasets reveal that, in the present, sedimentation is strongly influenced by deposition of laterally transported sediments sourced from the Mahalona River Delta. Variations in the amount of laterally transported sediments, as expressed by coarse fraction amounts in pelagic muds and turbidite recurrence rates and cumulative thicknesses, are primarily a function of lake-level induced delta slope instability and delta progradation into the basin. We infer lowest lake-levels between *29 and 16, a gradual lake level rise between *16 and 11, and high lake-levels between *11 and 0 kyr BP. Periods of highest turbidite deposition, *26 to 24 and *18 to Electronic supplementary material The online version of this article (
The tropical Pacific plays a fundamentally important role in global climate change due to the int... more The tropical Pacific plays a fundamentally important role in global climate change due to the interaction between the El Niño Southern Oscillation (ENSO), the Intertropical Convergence Zone (ITCZ), and the Asian monsoons. Indonesia sits at the heart of the tropical western Pacific, yet we have very few terrestrial paleoclimate records from Indonesia to evaluate hydrological changes in the tropical western
Proceedings of the National Academy of Sciences, 2014
Significance Climate variability in the tropical western Pacific exerts enormous influence on glo... more Significance Climate variability in the tropical western Pacific exerts enormous influence on global climate, yet its history remains poorly constrained. We present the region’s first continuous terrestrial sedimentary record of surface hydrology and vegetation spanning the last 60,000 y based upon geochemical data from Lake Towuti, Indonesia. Our data demonstrate that wet conditions and rainforest ecosystems present during the Holocene and during marine isotope stage 3 were interrupted by severe drying between ∼33,000 and 16,000 y B.P., when high-latitude ice sheets expanded and global temperatures cooled. These findings indicate an important role for glacial boundary conditions in pacing tropical western Pacific climate change, and highlight the potential for the western Pacific to amplify global climate change during glacial–interglacial cycles.
ABSTRACT Indonesia sits at the western edge of the tropical Pacific warm pool, and its climate re... more ABSTRACT Indonesia sits at the western edge of the tropical Pacific warm pool, and its climate responds to the Australasian monsoon and the intertropical convergence zone (ITCZ). Despite Indonesia&#39;s climatological significance, we have very few records of the region&#39;s hydrology. To fill this gap, in 2010 we collected long sediment piston cores and seismic reflection data from Lake Towuti, Sulawesi (2.5 S, 121 E), the largest lake in Indonesia. We are building new reconstructions of regional hydrology based upon sedimentological, geochemical, magnetic, core-scanning x-ray fluorescence, and compound-specific stable isotopic data to develop the first continuous record of rainfall and drought over the last 60,000 years from the maritime continent. Our record shows that, at the orbital scale, the boreal winter monsoon-dominated climate of central Indonesia responds to both precessional forcing of the Australasian monsoon and high latitude glacial processes. We observe relatively dry conditions at 60 kyr BP, wet conditions during much of Marine Isotope Stage 3 (MIS3), and a dry early/wet late Holocene. This is antiphased with speleothem 18O/16O records from China (e.g. Wang et al., 2008, Nature 451: 1090-1093), and is consistent with southward migration of the ITCZ over Indonesia and Australia during precession maxima. However, we observe the driest conditions of the last 60 kyr during the last glacial maximum (LGM), when southern hemisphere summer insolation was low. Previous studies (e.g. Griffiths et al., 2009, Nature Geosciences 2: 636-639) have suggested that exposure of the Sunda Shelf during the LGM reduces central Indonesian convection. However, we observe little effect of Sunda Shelf exposure on Indonesian hydrology during MIS3, and the deglacial rise in precipitation appears rapid in our data relative to sea level rise. We suggest that cool sea surface temperatures in the maritime continent, driven by greenhouse gas minima and associated glacial processes, reduced LGM convection over Indonesia. We observe substantial millennial-scale variability during MIS3 as well as the last glacial termination. For instance, Heinrich event 1 is a prominent arid event, as is the Younger Dryas. Aridity in central Indonesia during these North Atlantic stadials indicates that the &quot;northern mode&quot; of millennial climate variability observed in mainland Asia propagates south of the equator over maritime Indonesia, despite clear evidence for southward migration of the ITCZ. This suggests that water vapor content and convection within the ITCZ controls central Indonesian hydrology more than ITCZ position.
More than 100 km of seismic reflection profiles together with a new multibeam survey of the sedim... more More than 100 km of seismic reflection profiles together with a new multibeam survey of the sediment fill in lake Hestvatn, South Iceland, reveal two sub-basins filled with up to 44 m of deglacial and Holocene sediment. The chronology is constrained by geochemically characterized tephra layers and radiocarbon dates on marine molluscs. The Vedde Ash and Saksunarvatn Ash provide key chronological control for the deglacial sediment. Five seismic units are tied to the lithostratigraphy of sediment cores obtained from the two basins. The seismic units reveal major changes from glacial, to glacial-marine, to lacustrine sedimentary environments. Isopach maps of the seismic units document changes in the primary sediment depocenters, sedimentation rates and sediment delivery through time. The Vedde Ash, found only in glacial-marine sediment in the southern basin, suggests that during the Younger Dryas the northern basin of Hestvatn was occupied by an outlet glacier from the main Icelandic Ice Sheet that calved into a marine embayment. A high-resolution multibeam bathymetric survey reveals multiple shallow ridges between the two sub-basins of Hestvatn, which presumably acted as a pinning point for the calving glacier. During and after the retreat of the glacier and isolation of the lake basin, lacustrine sediments were mainly deposited via northern and northwesterly inlets, resulting in higher sedimentation rates in the north basin compared to the south basin. Early in the lacustrine phase repeated turbidites were deposited, interpreted to originate in glacial outburst floods (jökulhlaups) following a retreating ice-margin in central Iceland.
Glaciers often terminate in lakes, where they may form prominent moraines, and are considered rel... more Glaciers often terminate in lakes, where they may form prominent moraines, and are considered relatively stable. During the Little Ice Age (LIA: ca 1300-1900AD), strong regional cooling across the northern North Atlantic led to widespread glacier advances. At its peak, summer temperatures in Iceland are estimated to have been 3 to 4 °C lower than during the early Holocene optimum
Efforts to restore self-sustaining lake trout (Salvelinus namaycush) populations in the Laurentia... more Efforts to restore self-sustaining lake trout (Salvelinus namaycush) populations in the Laurentian Great Lakes have had widespread success in Lake Superior; but in other Great Lakes, populations of lake trout are maintained by stocking. Recruitment bottlenecks may be present at a number of stages of the reproduction process. To study eggs and fry, it is necessary to identify spawning locations,
The tropical western Pacific Ocean exerts a dominant influence on the Earth's atmospheric hea... more The tropical western Pacific Ocean exerts a dominant influence on the Earth's atmospheric heat and moisture budgets. Continental drilling of lake deposits through DOSECC and ICDP has begun to provide critical new information on the Plio-Pleistocene history of tropical continental climate, yet no potential drilling sites have been identified in the tropical western Pacific. Here we report results from the first seismic reflection studies ever conducted on large lakes in Indonesia that highlight the potential of Lake Towuti, South Sulawesi, for obtaining long terrestrial records of western Pacific climate. We have collected nearly 500 km of high-resolution seismic reflection (CHIRP) data from Lakes Matano (164 km2, 590 m deep) and Towuti (560 km2, 203 m deep), two of the Malili Lakes in central Sulawesi. These tectonic lakes formed about 2 Myr BP, and thus have the potential to provide long records of Indonesian climate. Seismic stratigraphic analyses of sediments from Lake Matano...
A series of airgun single-channel seismic-reflection profiles from Thunder Bay and the adjacent I... more A series of airgun single-channel seismic-reflection profiles from Thunder Bay and the adjacent Isle Royal Trough of Lake Superior suggest that water from Glacial Lake Agassiz did not catastrophically drain into Lake Superior at this locality, as has been previously suggested. Thunder Bay is underlain by a relatively smooth bedrock surface, the double bedrock sill at its mouth is not
ABSTRACT In the very fine-grained, gas-poor sediments of Lake Superior, it is possible to collect... more ABSTRACT In the very fine-grained, gas-poor sediments of Lake Superior, it is possible to collect extremely high resolution images of the subsurface with a 28 kHz echosounder. Penetration depths routinely exceed 20 m. This represents a significant portion of the lake&#39;s soft sediment section and makes it possible to image sediments that were deposited during the most recent de-glaciation of the basin. A high-resolution &quot;pseudo-3D&quot; seismic survey recently collected with this system in western Lake Superior provides convincing evidence of buried iceberg scouring in the lakefloor glaciolacustrine sediments. In seismic profiles, the scour appears as localized regions of acoustical blanking that are frequently &quot;U&quot; or &quot;V&quot;-shaped. The scour zones are typically 10s of meters across and up to 6 m deep. In plan-view, they exhibit a curvilinear appearance, frequently running for several kilometers. Many of the scour marks exhibit a WNW-ESE orientation, suggesting that the prevailing winds blew in this direction. Additional support for the iceberg-grounding interpretation is apparent from localized stratigraphic unconformities and raised lateral berms, interpreted to have been caused by iceberg- induced erosion and deformation of the ancient lake floor. By using the top of the scour marks as indicator of their relative age, it appears that the rate of calving into the lake changed over time, reaching a maximum shortly before the end of deposition of the red varved glaciolacustrine clays. Presumably this marks the final retreat of the Superior Lobe of the Laurentide Ice Sheet out of the lake. Earlier increases in scouring events, recorded in the sub-surface section are most likely the result of increases in calving during earlier minor readvances of the ice sheet.
ABSTRACT Glacial Lake Agassiz was the largest of the proglacial lakes to have formed in North Ame... more ABSTRACT Glacial Lake Agassiz was the largest of the proglacial lakes to have formed in North America during retreat of the Laurentide Ice Sheet. The extent of Lake Agassiz was controlled by a combination of factors including topography, ice position and amount of isostatic rebound. Many of the changes in the outlet location of the lake have been interpreted to involve a catastrophic release of water. Evidence for some of these catastrophic floods are visible in both terrestrial and sub-lacustrine records. An influx of freshwater from Lake Agassiz to the North Atlantic from such floods has been suggested as a possible trigger for the initiation of the Younger Dryas cold interval. A series of airgun single-channel seismic-reflection profiles from Thunder Bay and the adjacent Isle Royal trough of Lake Superior suggest that water from Glacial Lake Agassiz did not catastrophically release into Lake Superior at this locality, as has been previously suggested. Seismic surveys from a region further north within Lake Superior identified characteristic features of a later catastrophic release of water, which occurred after the Marquette glacial redadvance ca. 9,500 14C yr BP. The younger identified features to the north include bedrock scour and large debris fans, neither of which are present in the Thunder Bay area. Given the similarity in geomorphic conditions in the two locations, similar features are expected if the same type of catastrophic event occurred. Therefore, the absence of such features suggests that Lake Agassiz did not drain catastrophically through Thunder Bay. Instead of catastrophic outflow features in the seismic records, a thick package of distinct seismic units occur in the Isle Royale trough, which suggest a complex history of ice retreat and readvance. Trough parallel profiles show a massive seismic package, which grades into more individually distinguishable units in the direction of general ice retreat. These units appear to represent grounding-line fans deposited by Marquette ice during its retreat through the trough.
ABSTRACT Glacial Lake Agassiz was the largest of the North American glacial margin lakes. Over it... more ABSTRACT Glacial Lake Agassiz was the largest of the North American glacial margin lakes. Over its 4,000 year existence, Lake Agassiz varied substantially in aerial extent and volume. This variability was a function of the fluctuating retreat pattern of the Laurentide Ice Sheet&#39;s southwestern margin, differential isostatic rebound of the North American crust, the topography of the land exposed by the retreating ice, and erosion of the various outlet channels draining the lake. These factors combined to form a history of Lake Agassiz punctuated by sudden and sometimes catastrophic rerouting of its drainage from one outlet channel to another. The amount and routing of Lake Agassiz discharge has become controversial. However, extensive onshore observations of Glacial Lake Agassiz discharge features have firmly established that northwestern Lake Superior was a major drainage route following the retreat of the Marquette glacial advance ca. 9,500 years 14C BP. We describe a high-resolution single channel seismic reflection dataset collected with a small airgun that we acquired to test our hypothesis that this drainage event (corresponding to the Nipigon Phase of Lake Agassiz) left diagnostic stratigraphic and geomorphic signatures beneath Lake Superior. The unique bathymetry of northwestern Lake Superior, where water depth plunges off Nipigon and Black Bays, makes this location ideal for the identification and characterization of the Post-Marquette depositional features. The steep and sudden drop-off from the shallow water bays into the deep offshore waters of the lake would have caused the high-velocity floods to slow and drop much of the sediment they were carrying. Our results confirm the existence of these sediment packages, which are now buried below a thin blanket of Holocene sediment. They form wedges of sediment that are thickest (some over 70 m thick) in the deep water area adjacent to the flood outlet. The apron of sediment thins lakeward and shore-parallel away from the outlet. The seismic character of the basal units of the apron, proximal to the outlet, is chaotic and only very weakly stratified suggesting that these deposits represent coarse sediment laid down during the initial stages of the flood when flow was presumably at its peak. These sediments are overlain and draped by a weakly stratified package that is more widely developed (extending lakeward beyond the bounds of our survey). We interpret this unit, which becomes more stratified and thinner lakeward, to represent the fine grained sediment associated with the latter stages of the flood when flow had eased.
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