Erik Brown - Academia.edu (original) (raw)

Papers by Erik Brown

Journal of Great Lakes Research, 2018

The biogeochemical functioning of large tropical lakes differs substantially from temperate lakes... more The biogeochemical functioning of large tropical lakes differs substantially from temperate lakes, yet remains poorly understood. We characterized the carbon, nitrogen, and phosphorus cycling in the water column and sediments of a deep meromictic tropical Lake Malawi (East Africa) by measuring geochemical distributions and compiling whole-lake geochemical budgets. Four locations (100 to 650 m water depth) were characterized. The results reveal that sediments contribute significantly to lake-wide biogeochemical budgets. Sedimentation rates have significantly increased in recent decades. While the export efficiency of organic matter from photic zone to deep sediments is low (14%), organic carbon is buried in the anoxic sediments with high efficiency (27-46%). Area-specific rates of carbon mineralization (4.1 mmol m −2 d −1) are similar to those in temperate well-oxygenated large lakes and marine sediments in similar water depths. Ammonium effluxes from sediments (0.44 mmol m −2 d −1) contribute 29% to the total nitrogen inputs into the water column, while sediment denitrification (0.035 mmol m −2 d −1) and burial of organic nitrogen (0.27 mmol m −2 d −1) remove 28% of total inputs in the lake. The recycling efficiency of phosphorus in anoxic sediments is high (73%). P effluxes average 0.037 mmol m −2 d −1 , suggesting a large and previously unquantified contribution (42%) to water column P inputs. The results underscore the importance of sediments in the geochemical budgets of even large lakes and suggest trends in lacustrine carbon cycling that hold across a wide range of environments.

Quaternary Science Reviews, 2018

Hydroclimate extremes are expected to become more frequent and intense with anthropogenic climate... more Hydroclimate extremes are expected to become more frequent and intense with anthropogenic climate forcing, but future El Niño-Southern Oscillation (ENSO) behavior is unclear. Understanding of extreme hydroclimate variability and magnitude prior to human-influences is limited by short instrumental records, however, continuous sedimentary archives of past hydroclimate variability can complement and extend these records. Laminated Santa Barbara Basin (SBB) sediment cores MV0508-33JPC, À21JPC, and À29JPC preserve annually-resolved, multi-centennial-scale precipitation records from Termination V (T V), the transition from glacial Marine Isotope Stage (MIS) 12 to interglacial MIS 11 at 424 ka. These records provide insights into the subtropical hydroclimate response to warming. Foraminiferal d 18 O variations indicate rapid warming and/or salinity changes, and were used to verify the T V age assignment. A paleoprecipitation proxy was developed using the first principal component of scanning XRF elemental counts (PC1), which has high loadings for siliciclastic sediment-associated elements K, Ti, and Si. Sedimentary laminae couplets identified in PC1 were annually-tuned to investigate T V paleoprecipitation variability, as modern SBB laminae represent annual deposits. Extreme flooding and decadal-to-centennial droughts were identified, with magnitudes exceeding modern observations. ENSO-like (2e7 year) paleoprecipitation periodicities coincide with wetter intervals, but ENSO variability is reduced during droughts. A 1500-year arid interval may be related to poleward shifting of general atmospheric circulation as ice sheets melted, such that the subtropical dry zone intersected California. Southern California paleoprecipitation reconstructions from past warm climates provide insight into precipitation variability and magnitude on interannual timescales, and can reduce uncertainties in predictions of interannual climate, including ENSO.

International Journal of Earth Sciences, 2021

Sedimentary stratigraphy of Lake Chalco (Central Mexico) during its formative stages

Revista Mexicana de Ciencias Geológicas, 2018

En los sistemas lacustres relativamente profundos y con un bajo contenido de oxígeno en la interf... more En los sistemas lacustres relativamente profundos y con un bajo contenido de oxígeno en la interfase agua-sedimento es común la preservación de sedimentos anualmente laminados (varvas), los cuales indican una estacionalidad marcada en los procesos de depósito. El objetivo de este trabajo es caracterizar una sección laminada del registro sedimentario del lago de Chalco, cuenca de México, que se presenta intercalada con sedimentos masivos, material volcaniclástico y 13 capas de lodo micrítico. Esta secuencia laminada se ubica entre los 122.5 y los 106 m de profundidad y se le ha asignado una edad mayor a 130 ka, periodo que coincide con el final del penúltimo máximo glacial, o Estadio Isotópico seis (EI 6). La caracterización de los sedimentos se realizó mediante la observación al microscopio estereoscópico, compuesto y petrográfico de preparaciones frotis para identificar los componentes de las láminas claras, láminas oscuras y capas de lodo micrítico; algunas láminas claras y osc...

Quaternary Geochronology, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

All in-text references underlined in blue are linked to publications on ResearchGate, letting you... more All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.

Science Advances

Although climate change is considered to have been a large-scale driver of African human evolutio... more Although climate change is considered to have been a large-scale driver of African human evolution, landscape-scale shifts in ecological resources that may have shaped novel hominin adaptations are rarely investigated. We use well-dated, high-resolution, drill-core datasets to understand ecological dynamics associated with a major adaptive transition in the archeological record ~24 km from the coring site. Outcrops preserve evidence of the replacement of Acheulean by Middle Stone Age (MSA) technological, cognitive, and social innovations between 500 and 300 thousand years (ka) ago, contemporaneous with large-scale taxonomic and adaptive turnover in mammal herbivores. Beginning ~400 ka ago, tectonic, hydrological, and ecological changes combined to disrupt a relatively stable resource base, prompting fluctuations of increasing magnitude in freshwater availability, grassland communities, and woody plant cover. Interaction of these factors offers a resource-oriented hypothesis for the ...

Palaeogeography, Palaeoclimatology, Palaeoecology, 2001

Scientific Drilling, 2012

This workshop report describes plans for scientific drilling in the Samail ophiolite in Oman in t... more This workshop report describes plans for scientific drilling in the Samail ophiolite in Oman in the context of past, current, and future research. Long-standing plans to study formation and evolution of the Samail crust and upper mantle, involving igneous and metamorphic processes at an oceanic spreading center, have been augmented by recent interest in ongoing, low temperature processes. These include alteration and weathering, and the associated sub-surface biosphere supported by chemical potential energy due to disequilibrium between mantle peridotite and water near the surface. This interest is motivated in part by the possibility of geological carbon capture and storage via engineered, accelerated mineral carbonation in Oman. Our International Continental Drilling Program (ICDP) proposal led to the Workshop on Scientific Drilling in the Samail Ophiolite in Palisades, New York, on 13-17 September 2012. There were seventy-seven attendees from eleven countries, including twenty early career scientists. After keynote presentations on overarching science themes, participants in working groups and plenary sessions outlined a ~U.S.$2 million drilling plan that practically addresses testable hypotheses and areas of frontier discovery in the following areas.

Proceedings of the National Academy of Sciences, 2007

The environmental backdrop to the evolution and spread of early Homo sapiens in East Africa is kn... more The environmental backdrop to the evolution and spread of early Homo sapiens in East Africa is known mainly from isolated outcrops and distant marine sediment cores. Here we present results from new scientific drill cores from Lake Malawi, the first long and continuous, high-fidelity records of tropical climate change from the continent itself. Our record shows periods of severe aridity between 135 and 75 thousand years (kyr) ago, when the lake's water volume was reduced by at least 95%. Surprisingly, these intervals of pronounced tropical African aridity in the early late-Pleistocene were much more severe than the Last Glacial Maximum (LGM), the period previously recognized as one of the most arid of the Quaternary. From these cores and from records from Lakes Tanganyika (East Africa) and Bosumtwi (West Africa), we document a major rise in water levels and a shift to more humid conditions over much of tropical Africa after ≈70 kyr ago. This transition to wetter, more stable con...

Proceedings of the National Academy of Sciences, 2007

Extremely arid conditions in tropical Africa occurred in several discrete episodes between 135 an... more Extremely arid conditions in tropical Africa occurred in several discrete episodes between 135 and 90 ka, as demonstrated by lake core and seismic records from multiple basins [Scholz CA, Johnson TC, Cohen AS, King JW, Peck J, Overpeck JT, Talbot MR, Brown ET, Kalindekafe L, Amoako PYO, et al. (2007) Proc Natl Acad Sci USA 104:16416–16421]. This resulted in extraordinarily low lake levels, even in Africa's deepest lakes. On the basis of well dated paleoecological records from Lake Malawi, which reflect both local and regional conditions, we show that this aridity had severe consequences for terrestrial and aquatic ecosystems. During the most arid phase, there was extremely low pollen production and limited charred-particle deposition, indicating insufficient vegetation to maintain substantial fires, and the Lake Malawi watershed experienced cool, semidesert conditions (<400 mm/yr precipitation). Fossil and sedimentological data show that Lake Malawi itself, currently 706 m de...

Palaeogeography, Palaeoclimatology, Palaeoecology, 2010

Lake Karakul in the Pamirs (Tajikistan) is a deep brackish-water lake in a closed basin at almost... more Lake Karakul in the Pamirs (Tajikistan) is a deep brackish-water lake in a closed basin at almost 4000 m above sea level. Water samples from the catchment area and Lake Karakul, and a 104-cm sediment core from its shallow eastern sub-basin, were investigated and provide ...

Chemical Geology, 2000

Depth profiles of in situ-produced cosniogenic nuclides, including "'Be (T,/? = 1.5 X IO6 years) ... more Depth profiles of in situ-produced cosniogenic nuclides, including "'Be (T,/? = 1.5 X IO6 years) and "Al (T,/,0.73 X lo6 years), in the upper few meters of the Earth's crust may be used to study surficial processes, quantifying denudation and burial rates and elucidating mechanism involved in landform evolution and soil formations. In this paper, we discuss the fundamentals of the method and apply it to two lateritic sequences located in African tropical forests.

Geophysical Research Letters, 2007

We performed a set of nutrient-enrichment bioassay experiments using metal-clean protocols, testi... more We performed a set of nutrient-enrichment bioassay experiments using metal-clean protocols, testing for mac-ronutrient and micronutrient limitation of algae and bacteria in western Lake Superior. Our analysis involved a novel approach to estimating the strength of nutrient limitation in factorial enrichment designs. We found that phytoplankton and bacterioplankton growth both increased with added phosphorus alone but not with iron, man-ganese, or zinc alone. However, even very small increases in growth rates following P supplementation (on the order of an additional 0.1 d21) induced iron limitation in the phytoplankton, indicating that the algae in this large lake may be on the cusp of micronutrient and macronutrient limitation. In contrast, and contrary to expectations, bacteria responded only to P and not to metals. Spatial and temporal variability in degree and quality of nutrient limitation was considerable. The recent surge of interest in the role of bioactive metals in control...

Geological Society of America Abstracts with Programs

Journal of Great Lakes Research, 2018

The biogeochemical functioning of large tropical lakes differs substantially from temperate lakes... more The biogeochemical functioning of large tropical lakes differs substantially from temperate lakes, yet remains poorly understood. We characterized the carbon, nitrogen, and phosphorus cycling in the water column and sediments of a deep meromictic tropical Lake Malawi (East Africa) by measuring geochemical distributions and compiling whole-lake geochemical budgets. Four locations (100 to 650 m water depth) were characterized. The results reveal that sediments contribute significantly to lake-wide biogeochemical budgets. Sedimentation rates have significantly increased in recent decades. While the export efficiency of organic matter from photic zone to deep sediments is low (14%), organic carbon is buried in the anoxic sediments with high efficiency (27-46%). Area-specific rates of carbon mineralization (4.1 mmol m −2 d −1) are similar to those in temperate well-oxygenated large lakes and marine sediments in similar water depths. Ammonium effluxes from sediments (0.44 mmol m −2 d −1) contribute 29% to the total nitrogen inputs into the water column, while sediment denitrification (0.035 mmol m −2 d −1) and burial of organic nitrogen (0.27 mmol m −2 d −1) remove 28% of total inputs in the lake. The recycling efficiency of phosphorus in anoxic sediments is high (73%). P effluxes average 0.037 mmol m −2 d −1 , suggesting a large and previously unquantified contribution (42%) to water column P inputs. The results underscore the importance of sediments in the geochemical budgets of even large lakes and suggest trends in lacustrine carbon cycling that hold across a wide range of environments.

Quaternary Science Reviews, 2018

Hydroclimate extremes are expected to become more frequent and intense with anthropogenic climate... more Hydroclimate extremes are expected to become more frequent and intense with anthropogenic climate forcing, but future El Niño-Southern Oscillation (ENSO) behavior is unclear. Understanding of extreme hydroclimate variability and magnitude prior to human-influences is limited by short instrumental records, however, continuous sedimentary archives of past hydroclimate variability can complement and extend these records. Laminated Santa Barbara Basin (SBB) sediment cores MV0508-33JPC, À21JPC, and À29JPC preserve annually-resolved, multi-centennial-scale precipitation records from Termination V (T V), the transition from glacial Marine Isotope Stage (MIS) 12 to interglacial MIS 11 at 424 ka. These records provide insights into the subtropical hydroclimate response to warming. Foraminiferal d 18 O variations indicate rapid warming and/or salinity changes, and were used to verify the T V age assignment. A paleoprecipitation proxy was developed using the first principal component of scanning XRF elemental counts (PC1), which has high loadings for siliciclastic sediment-associated elements K, Ti, and Si. Sedimentary laminae couplets identified in PC1 were annually-tuned to investigate T V paleoprecipitation variability, as modern SBB laminae represent annual deposits. Extreme flooding and decadal-to-centennial droughts were identified, with magnitudes exceeding modern observations. ENSO-like (2e7 year) paleoprecipitation periodicities coincide with wetter intervals, but ENSO variability is reduced during droughts. A 1500-year arid interval may be related to poleward shifting of general atmospheric circulation as ice sheets melted, such that the subtropical dry zone intersected California. Southern California paleoprecipitation reconstructions from past warm climates provide insight into precipitation variability and magnitude on interannual timescales, and can reduce uncertainties in predictions of interannual climate, including ENSO.

International Journal of Earth Sciences, 2021

Sedimentary stratigraphy of Lake Chalco (Central Mexico) during its formative stages

Revista Mexicana de Ciencias Geológicas, 2018

En los sistemas lacustres relativamente profundos y con un bajo contenido de oxígeno en la interf... more En los sistemas lacustres relativamente profundos y con un bajo contenido de oxígeno en la interfase agua-sedimento es común la preservación de sedimentos anualmente laminados (varvas), los cuales indican una estacionalidad marcada en los procesos de depósito. El objetivo de este trabajo es caracterizar una sección laminada del registro sedimentario del lago de Chalco, cuenca de México, que se presenta intercalada con sedimentos masivos, material volcaniclástico y 13 capas de lodo micrítico. Esta secuencia laminada se ubica entre los 122.5 y los 106 m de profundidad y se le ha asignado una edad mayor a 130 ka, periodo que coincide con el final del penúltimo máximo glacial, o Estadio Isotópico seis (EI 6). La caracterización de los sedimentos se realizó mediante la observación al microscopio estereoscópico, compuesto y petrográfico de preparaciones frotis para identificar los componentes de las láminas claras, láminas oscuras y capas de lodo micrítico; algunas láminas claras y osc...

Quaternary Geochronology, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

All in-text references underlined in blue are linked to publications on ResearchGate, letting you... more All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.

Science Advances

Although climate change is considered to have been a large-scale driver of African human evolutio... more Although climate change is considered to have been a large-scale driver of African human evolution, landscape-scale shifts in ecological resources that may have shaped novel hominin adaptations are rarely investigated. We use well-dated, high-resolution, drill-core datasets to understand ecological dynamics associated with a major adaptive transition in the archeological record ~24 km from the coring site. Outcrops preserve evidence of the replacement of Acheulean by Middle Stone Age (MSA) technological, cognitive, and social innovations between 500 and 300 thousand years (ka) ago, contemporaneous with large-scale taxonomic and adaptive turnover in mammal herbivores. Beginning ~400 ka ago, tectonic, hydrological, and ecological changes combined to disrupt a relatively stable resource base, prompting fluctuations of increasing magnitude in freshwater availability, grassland communities, and woody plant cover. Interaction of these factors offers a resource-oriented hypothesis for the ...

Palaeogeography, Palaeoclimatology, Palaeoecology, 2001

Scientific Drilling, 2012

This workshop report describes plans for scientific drilling in the Samail ophiolite in Oman in t... more This workshop report describes plans for scientific drilling in the Samail ophiolite in Oman in the context of past, current, and future research. Long-standing plans to study formation and evolution of the Samail crust and upper mantle, involving igneous and metamorphic processes at an oceanic spreading center, have been augmented by recent interest in ongoing, low temperature processes. These include alteration and weathering, and the associated sub-surface biosphere supported by chemical potential energy due to disequilibrium between mantle peridotite and water near the surface. This interest is motivated in part by the possibility of geological carbon capture and storage via engineered, accelerated mineral carbonation in Oman. Our International Continental Drilling Program (ICDP) proposal led to the Workshop on Scientific Drilling in the Samail Ophiolite in Palisades, New York, on 13-17 September 2012. There were seventy-seven attendees from eleven countries, including twenty early career scientists. After keynote presentations on overarching science themes, participants in working groups and plenary sessions outlined a ~U.S.$2 million drilling plan that practically addresses testable hypotheses and areas of frontier discovery in the following areas.

Proceedings of the National Academy of Sciences, 2007

The environmental backdrop to the evolution and spread of early Homo sapiens in East Africa is kn... more The environmental backdrop to the evolution and spread of early Homo sapiens in East Africa is known mainly from isolated outcrops and distant marine sediment cores. Here we present results from new scientific drill cores from Lake Malawi, the first long and continuous, high-fidelity records of tropical climate change from the continent itself. Our record shows periods of severe aridity between 135 and 75 thousand years (kyr) ago, when the lake's water volume was reduced by at least 95%. Surprisingly, these intervals of pronounced tropical African aridity in the early late-Pleistocene were much more severe than the Last Glacial Maximum (LGM), the period previously recognized as one of the most arid of the Quaternary. From these cores and from records from Lakes Tanganyika (East Africa) and Bosumtwi (West Africa), we document a major rise in water levels and a shift to more humid conditions over much of tropical Africa after ≈70 kyr ago. This transition to wetter, more stable con...

Proceedings of the National Academy of Sciences, 2007

Extremely arid conditions in tropical Africa occurred in several discrete episodes between 135 an... more Extremely arid conditions in tropical Africa occurred in several discrete episodes between 135 and 90 ka, as demonstrated by lake core and seismic records from multiple basins [Scholz CA, Johnson TC, Cohen AS, King JW, Peck J, Overpeck JT, Talbot MR, Brown ET, Kalindekafe L, Amoako PYO, et al. (2007) Proc Natl Acad Sci USA 104:16416–16421]. This resulted in extraordinarily low lake levels, even in Africa's deepest lakes. On the basis of well dated paleoecological records from Lake Malawi, which reflect both local and regional conditions, we show that this aridity had severe consequences for terrestrial and aquatic ecosystems. During the most arid phase, there was extremely low pollen production and limited charred-particle deposition, indicating insufficient vegetation to maintain substantial fires, and the Lake Malawi watershed experienced cool, semidesert conditions (<400 mm/yr precipitation). Fossil and sedimentological data show that Lake Malawi itself, currently 706 m de...

Palaeogeography, Palaeoclimatology, Palaeoecology, 2010

Lake Karakul in the Pamirs (Tajikistan) is a deep brackish-water lake in a closed basin at almost... more Lake Karakul in the Pamirs (Tajikistan) is a deep brackish-water lake in a closed basin at almost 4000 m above sea level. Water samples from the catchment area and Lake Karakul, and a 104-cm sediment core from its shallow eastern sub-basin, were investigated and provide ...

Chemical Geology, 2000

Depth profiles of in situ-produced cosniogenic nuclides, including "'Be (T,/? = 1.5 X IO6 years) ... more Depth profiles of in situ-produced cosniogenic nuclides, including "'Be (T,/? = 1.5 X IO6 years) and "Al (T,/,0.73 X lo6 years), in the upper few meters of the Earth's crust may be used to study surficial processes, quantifying denudation and burial rates and elucidating mechanism involved in landform evolution and soil formations. In this paper, we discuss the fundamentals of the method and apply it to two lateritic sequences located in African tropical forests.

Geophysical Research Letters, 2007

We performed a set of nutrient-enrichment bioassay experiments using metal-clean protocols, testi... more We performed a set of nutrient-enrichment bioassay experiments using metal-clean protocols, testing for mac-ronutrient and micronutrient limitation of algae and bacteria in western Lake Superior. Our analysis involved a novel approach to estimating the strength of nutrient limitation in factorial enrichment designs. We found that phytoplankton and bacterioplankton growth both increased with added phosphorus alone but not with iron, man-ganese, or zinc alone. However, even very small increases in growth rates following P supplementation (on the order of an additional 0.1 d21) induced iron limitation in the phytoplankton, indicating that the algae in this large lake may be on the cusp of micronutrient and macronutrient limitation. In contrast, and contrary to expectations, bacteria responded only to P and not to metals. Spatial and temporal variability in degree and quality of nutrient limitation was considerable. The recent surge of interest in the role of bioactive metals in control...

Geological Society of America Abstracts with Programs