Jens Zinke | Freie Universität Berlin (original) (raw)

Papers by Jens Zinke

The ability of massive Porites corals to faithfully record temperature is assessed. Porites coral... more The ability of massive Porites corals to faithfully record temperature is assessed. Porites corals from Kepulauan Seribu were sampled from one inshore and one offshore site and analyzed for their Sr/Ca variation. The results show that Sr/Ca of the offshore coral tracked SST, while Sr/Ca variation of the inshore coral tracked ambient air temperature. In particular, the inshore SST variation is related to air temperature anomalies of the urban center of Jakarta. The latter we relate to air—sea interactions modifying inshore SST associated with the land-sea breeze mechanism and/or monsoonal circulation. The correlation pattern of monthly coral Sr/Ca with the Niño3.4 index and SEIO-SST reveals that corals in the Seribu islands region respond differently to remote forcing. An opposite response is observed for inshore and offshore corals in response to El Niño onset, yet similar to El Niño mature phase (December to February). SEIO SSTs co-vary strongly with SST and air temperature variability across the Seribu island reef complex. The results of this study clearly indicate that locations of coral proxy record in Indonesia need to be chosen carefully in order to identify the seasonal climate response to local and remote climate and anthropogenic forcing.

response to ENSO is important. ENSO, in the absence of the SIOD, forces an equivalent barotropic ... more response to ENSO is important. ENSO, in the absence of the SIOD, forces an equivalent barotropic Rossby wave over Southern Africa that modifies the regional mid-tropospheric vertical motions and precipitation anomalies. El Niño (La Niña) is related with high (low) pressure over Southern Africa that produces anomalous mid-tropospheric descent (ascent) and decreases (increases) in precipitation relative to average. When the SIOD and ENSO are in opposite phases, the SIOD compliments the ENSO-related atmospheric response over Southern Africa by strengthening the regional equivalent barotropic Rossby wave, anomalous mid-tropo-spheric vertical motions and anomalous precipitation. By contrast, when the SIOD and ENSO are in the same phase, the SIOD disrupts the ENSO-related atmospheric response over Southern Africa by weakening the regional equivalent barotropic Rossby wave, anomalous mid-tropospheric vertical motions and anomalous precipitation.

The western Indian Ocean has been warming rapidly over recent decades, causing a greater number o... more The western Indian Ocean has been warming rapidly over recent decades, causing a greater number of extreme climatic events. It is therefore of paramount importance to improve our understanding of links between In-dian Ocean sea surface temperature (SST) variability, climate change and sustainability of tropical coral reef ecosystems. Here we present monthly resolved coral Sr / Ca records from two different locations from Rodrigues Island (63 • E, 19 • S) in the south-central Indian Ocean trade wind belt. We reconstruct SST based on a linear relationship with the Sr / Ca proxy with records starting from 1781 and 1945, respectively. We assess relationships between the observed long-term SST and climate fluctuations related to the El Niño–Southern Oscillation (ENSO), the Subtropical Indian Ocean Dipole Mode (SIOD) and the Pacific Decadal Oscillation (PDO) between 1945 and 2006, respectively. The reproducibility of the Sr / Ca records is assessed as are the potential impacts of diagenesis and corallite orientation on Sr / Ca–SST reconstructions. We calibrate individual robust Sr / Ca records with in situ SST and various gridded SST products. The results show that the SST record from Cabri provides the first Indian Ocean coral proxy time series that records the SST signature of the PDO in the south-central Indian Ocean since 1945. We suggest that additional records from Rodrigues Island can provide excellent records of SST variations in the southern Indian Ocean trade wind belt to unravel teleconnections with the SIOD/ENSO/PDO on longer timescales.

During the summer of 2010/2011, a regional marine heat wave resulted in coral bleaching of variab... more During the summer of 2010/2011, a regional marine heat wave resulted in coral bleaching of variable severity along much of the western coastline of Australia. At Ningaloo Reef, a 300 km long fringing reef system and World Heritage site, highly contrasting coral bleaching was observed between two morphologically distinct nearshore reef communities located on either side of the Ningaloo Peninsula: Tantabiddi (20% bleaching) and Bundegi (90% bleaching). For this study, we collected coral cores (Porites sp.) from Tantabiddi and Bundegi reef sites to assess the response of the Sr/Ca temperature proxy and Mg/Ca ratios to the variable levels of thermal stress imposed at these two sites during the 2010/2011 warming event. We found that there was an anomalous increase in Sr/Ca and decrease in Mg/Ca ratios in the Bundegi record that was coincident with the timing of severe coral bleaching at the site, while no significant changes were observed in the Tantabiddi record. We show that the change in the relationship of Sr/Ca and Mg/Ca ratios with temperature at Bundegi during the 2010/2011 event reflects changes in related coral ''vital'' processes during periods of environmental stress. These changes were found to be consistent with a reduction in active transport of Ca 21 to the site of calcification leading to a reduction in calcification rates and reduced Rayleigh fractionation of incorporated trace elements. Plain Language Summary In this paper, we compare coral-core geochemical records (Sr/Ca and Mg/Ca) from two reef sites at Ningaloo Reef, Western Australia, which showed highly contrasting coral bleaching severities following a regional heat wave during the summer of 2010/11. We show that anomalous increases in Sr/Ca ratios and decreases in Mg/Ca ratios can provide a distinct signature of past thermal stress events making core records useful for understanding the variable impacts of regional ocean warming events within reef ecosystems. Furthermore, by using a novel approach we were able to explain the formation of these anomalies during periods of thermal stress through changes in coral physiological and kinetic processes, which, along with temperature, also effect the incorporation of trace elements in coral skeleton. This is of particular importance as coral core records are heavily relied upon for the understanding of climate change, yet the mechanisms responsible for acute changes in coral trace element ratios during periods of thermal stress have previously not been discussed. We thus hope our work will contribute to the understanding of coral physiology and the development of more robust records of climate change in the future.

Coral reefs are biologically diverse ecosystems threatened with effective collapse under rapid cl... more Coral reefs are biologically diverse ecosystems threatened with effective collapse under rapid climate change, in particular by recent increases in ocean temperatures. Coral bleaching has occurred during major El Niño warming events, at times leading to the die-off of entire coral reefs. Here we present records of stable isotopic composition, Sr/Ca ratios and extension rate (1940–2004) in coral aragonite from a northern Venezuelan site, where reefs were strongly impacted by bleaching following the 1997–98 El Niño. We assess the impact of past warming events on coral extension rates and geochemical proxies. A marked decrease in coral (Pseudodiploria strigosa) extension rates coincides with a baseline shift to more negative values in oxygen and carbon isotopic composition after 1997–98, while a neighboring coral (Siderastrea siderea) recovered to pre-bleaching extension rates simultaneously. However, other stressors, besides high temperature, might also have influenced coral physiology and geochemistry. Coastal Venezuelan reefs were exposed to a series of extreme environmental fluctuations since the mid-1990s, i.e. upwelling, extreme rainfall and sediment input from landslides. This work provides important new data on the potential impacts of multiple regional stress events on coral isotopic compositions and raises questions about the long-term influence on coral-based paleoclimate reconstructions. Under projected anthropogenic climate change scenarios the widespread destruction of tropical coral reef ecosystems will become a reality over the next decades 1. Current models forecast an increase in average global surface temperatures of at least 2 °C by 2100 relative to the pre-industrial period and up to 3–4 °C under existing patterns of human activity 2. Around 30–50% of worldwide coral reefs have been largely or completely degraded due to the combined effects of local factors and global climate change during recent decades 3. Water temperature is one of the most important variables limiting the growth and distribution of reef-building corals 4. Shallow water tropical corals grow within a temperature range of around 18–30 °C 5. Since the early 1980s sea surface temperatures (SSTs) have rapidly increased and tropical corals have experienced large-scale bleaching and mortality events 6. During periods of sustained high temperature, bleaching occurs, a process during which the symbiosis between corals and their photosynthetic microalgae that live within their cells breaks down. Subsequently, the loss of the symbiotic algae causes whitening (" bleaching ") of the coral tissue 7,8 and leads to their starvation, and in many cases to disease and mortality. For example, in 1998, following a super El Niño high temperature event, widespread coral bleaching and mortality was observed and approximately 16% of the worldwide coral communities bleached and died 8. Climate-induced coral bleaching is one of the most serious threats to present-day coral reefs 9. The Caribbean was heavily impacted by El Niño-related bleaching events in 1995, 1997/98, 2005 10 and 2010. Simultaneously, coastal Venezuelan reefs and marine communities were exposed to a series of extreme

Episodic anomalously warm sea surface temperature (SST) extremes, or marine heatwaves (MHWs), amp... more Episodic anomalously warm sea surface temperature (SST) extremes, or marine heatwaves (MHWs), amplify ocean warming effects and may lead to severe impacts on marine ecosystems. MHW-induced coral bleaching events have been observed frequently in recent decades in the southeast Indian Ocean (SEIO), a region traditionally regarded to have resilience to global warming. In this study, we assess the contribution of El Niño-Southern Oscillation (ENSO) to MHWs across the mostly understudied reefs in the SEIO. We find that in extended summer months, the MHWs at tropical and subtropical reefs (divided at ~20°S) are driven by opposite ENSO polarities: MHWs are more likely to occur at the tropical reefs during eastern Pacific El Niño, driven by enhanced solar radiation and weaker Australian Monsoon, some likely alleviated by positive Indian Ocean Dipole events, and at the subtropical reefs during central Pacific La Niña, mainly caused by increased horizontal heat transport, and in some cases reinforced by local air-sea interactions. Madden-Julian Oscillations (MJO) also modulate the MHW occurrences. Projected future increases in ENSO and MJO intensity with greenhouse warming will enhance thermal stress across the SEIO. Implementing forecasting systems of MHWs can be used to anticipate future coral bleaching patterns and prepare management responses.

GKSS School of Environmental Research, 2004

... available within KIHZ KIHZ-Consortium: J. Zinke 1 , H. von Storch 2 , B. Müller 2 , E. Zorita... more ... available within KIHZ KIHZ-Consortium: J. Zinke 1 , H. von Storch 2 , B. Müller 2 , E. Zorita 2 , B. Rein 3 , H. B. Mieding 4 , H. Miller 4 , A. Lücke 5 , GH Schleser 5 , MJ Schwab 6 , JFW Negendank 6 , U. Kienel 6 ,JF González -Ruoco 8 , Christian Dullo 1 , Anton Eisenhauer 1 ...

Geochemistry, Geophysics, Geosystems, 2011

Many marine fishes have life history strategies that involve ontogenetic changes in the use of co... more Many marine fishes have life history strategies that involve ontogenetic changes in the use of coastal habitats. Such ontogenetic shifts may place these species at particular risk from climate change, because the successive environments they inhabit can differ in the type, frequency and severity of changes related to global warming. We used a dendrochronology approach to examine the physical and biological drivers of growth of adult and juvenile mangrove jack (Lutjanus argentimaculatus) from tropical north-western Australia. Juveniles of this species inhabit estuarine environments and adults reside on coastal reefs. The Niño-4 index, a measure of the status of the El Niño-Southern Oscillation (ENSO) had the highest correlation with adult growth chronologies, with La Niña years (characterised by warmer temperatures and lower salinities) having positive impacts on growth. Atmospheric and oceanographic phenomena operating at ocean-basin scales seem to be important correlates of the processes driving growth in local coastal habitats. Conversely, terrestrial factors influencing precipitation and river runoff were positively correlated with the growth of juveniles in estuaries. Our results show that the impacts of climate change on these two life history stages are likely to be different, with implications for resilience and management of populations.

We report fossil coral records from the Sey- chelles comprising individual time slices of 14–20 s... more We report fossil coral records from the Sey- chelles comprising individual time slices of 14–20 sclero- chronological years between 2 and 6.2kyr BP to reconstruct changes in the seasonal cycle of western Indian Ocean sea surface temperature (SST) compared to the present (1990–2003). These reconstructions allowed us to link changes in the SST bimodality to orbital changes, which were causing a reorganization of the seasonal inso- lation pattern. Our results reveal the lowest seasonal SST range in the Mid-Holocene (6.2–5.2 kyr BP) and around kyr BP, while the highest range is observed around 4.6 kyr BP and between 1990 and 2003. The season of maximum temperature shifts from austral spring (Septem- ber to November) to austral autumn (March to May), fol- lowing changes in seasonal insolation over the past 6 kyr. However, the changes in SST bimodality do not linearly follow the insolation seasonality. For example, the 5.2 and 6.2 kyr BP corals show only subtle SST differences in austral spring and autumn. We use paleoclimate simula- tions of a fully coupled atmosphere–ocean general circu- lation model to compare with proxy data for the Mid- Holocene around 6 kyr BP. The model results show that in the Mid-Holocene the austral winter and spring seasons in the western Indian Ocean were warmer while austral summer was cooler. This is qualitatively consistent with the coral data from 6.2 to 5.2 kyr BP, which shows a similar reduction in the seasonal amplitude compared to the present day. However, the pattern of the seasonal SST cycle in the model appears to follow the changes in inso- lation more directly than indicated by the corals. Our results highlight the importance of ocean–atmosphere interactions for Indian Ocean SST seasonality throughout the Holocene. In order to understand Holocene climate variability in the countries surrounding the Indian Ocean, we need a much more comprehensive analysis of season- ally resolved archives from the tropical Indian Ocean. Insolation data alone only provides an incomplete picture.

A wide range of sea surface temperature (SST) expressions have been observed during the El Niño–S... more A wide range of sea surface temperature (SST) expressions have been observed during the El Niño–South- ern Oscillation events of 1950–2010, which have occurred simultaneously with different global atmospheric circu- lations. This study examines the atmospheric circulation and precipitation during December–March 1950–2010 over the African Continent south of 15 S, a region hereaf- ter known as Southern Africa, associated with eight tropi- cal Pacific SST expressions characteristic of El Niño and La Niña events. The self-organizing map method along with a statistical distinguishability test was used to isolate the SST expressions of El Niño and La Niña. The seasonal precipitation forcing over Southern Africa associated with the eight SST expressions was investigated in terms of the horizontal winds, moisture budget and vertical motion. El Niño events, with warm SST across the east and cen- tral Pacific Ocean and warmer than average SST over the Indian Ocean, are associated with precipitation reductions over Southern Africa. The regional precipitation reduc- tions are forced primarily by large-scale mid-tropospheric subsidence associated with anticyclonic circulation in the upper troposphere. El Niño events with cooler than average SST over the Indian Ocean are associated with precipita- tion increases over Southern Africa associated with lower tropospheric cyclonic circulation and mid-tropospheric ascent. La Niña events, with cool SST anomalies over the central Pacific and warm SST over the west Pacific and Indian Ocean, are associated with precipitation increases over Southern Africa. The regional precipitation increases are forced primarily by lower tropospheric cyclonic circula- tion, resulting in mid-tropospheric ascent and an increased flux of moisture into the region.

Paleoclimate reconstructions based on reef corals require precise detection of diagenetic alterat... more Paleoclimate reconstructions based on reef corals require precise detection of diagenetic alteration. Secondary calcite can significantly affect paleotemperature reconstructions at very low amounts of 􏰀1%. X-ray powder diffraction is routinely used to detect diagenetic calcite in aragonitic corals. This procedure has its limitations as single powder samples might not represent the entire coral heterogeneity. A conventional and a 2-D X-ray diffractometer were calibrated with gravimetric powder standards of high and low magnesium calcite (0.3% to 25% calcite). Calcite contents <1% can be recognized with both diffractometer setups based on the peak area of the calcite [104] reflection. An advantage of 2-D-XRD over convenient 1-D-XRD methods is the nondestructive and rapid detection of calcite with relatively high spatial resolution directly on coral slabs. The calcite detection performance of the 2-D-XRD setup was tested on thin sections from fossil Porites sp. samples that, based on powder XRD measurements, showed <1% calcite. Quantification of calcite contents for these thin sections based on 2-D-XRD and digital image analysis showed very similar results. This enables spot measurements with diameters of 􏰀4 mm, as well as systematic line scans along potential tracks previous to geochemical proxy sampling. In this way, areas affected by diagenetic calcite can be avoided and alternative sam- pling tracks can be defined. Alternatively, individual sampling positions that show dubious proxy results can later be checked for the presence of calcite. The presented calibration and quantification method can be transferred to any 2-D X-ray diffractometer.

Increasing intensity of marine heatwaves has caused widespread mass coral bleaching events, threa... more Increasing intensity of marine heatwaves has caused widespread mass coral bleaching events, threatening the integrity and functional diversity of coral reefs. Here we demonstrate the role of inter-ocean coupling in amplifying thermal stress on reefs in the poorly studied southeast Indian Ocean (SEIO), through a robust 215-year (1795–2010) geochemical coral proxy sea surface temperature (SST) record. We show that marine heatwaves affecting the SEIO are linked to the behaviour of the Western Pacific Warm Pool on decadal to centennial timescales, and are most pronounced when an anomalously strong zonal SST gradient between the western and central Pacific co-occurs with strong La Nin ̃a’s. This SST gradient forces large-scale changes in heat flux that exacerbate SEIO heatwaves. Better understanding of the zonal SST gradient in the Western Pacific is expected to improve projections of the frequency of extreme SEIO heatwaves and their ecological impacts on the important coral reef ecosystems off Western Australia.

Computer Methods in Biomechanics and Biomedical Engineering, 2011

The ability of massive Porites corals to faithfully record temperature is assessed. Porites coral... more The ability of massive Porites corals to faithfully record temperature is assessed. Porites corals from Kepulauan Seribu were sampled from one inshore and one offshore site and analyzed for their Sr/Ca variation. The results show that Sr/Ca of the offshore coral tracked SST, while Sr/Ca variation of the inshore coral tracked ambient air temperature. In particular, the inshore SST variation is related to air temperature anomalies of the urban center of Jakarta. The latter we relate to air—sea interactions modifying inshore SST associated with the land-sea breeze mechanism and/or monsoonal circulation. The correlation pattern of monthly coral Sr/Ca with the Niño3.4 index and SEIO-SST reveals that corals in the Seribu islands region respond differently to remote forcing. An opposite response is observed for inshore and offshore corals in response to El Niño onset, yet similar to El Niño mature phase (December to February). SEIO SSTs co-vary strongly with SST and air temperature variability across the Seribu island reef complex. The results of this study clearly indicate that locations of coral proxy record in Indonesia need to be chosen carefully in order to identify the seasonal climate response to local and remote climate and anthropogenic forcing.

response to ENSO is important. ENSO, in the absence of the SIOD, forces an equivalent barotropic ... more response to ENSO is important. ENSO, in the absence of the SIOD, forces an equivalent barotropic Rossby wave over Southern Africa that modifies the regional mid-tropospheric vertical motions and precipitation anomalies. El Niño (La Niña) is related with high (low) pressure over Southern Africa that produces anomalous mid-tropospheric descent (ascent) and decreases (increases) in precipitation relative to average. When the SIOD and ENSO are in opposite phases, the SIOD compliments the ENSO-related atmospheric response over Southern Africa by strengthening the regional equivalent barotropic Rossby wave, anomalous mid-tropo-spheric vertical motions and anomalous precipitation. By contrast, when the SIOD and ENSO are in the same phase, the SIOD disrupts the ENSO-related atmospheric response over Southern Africa by weakening the regional equivalent barotropic Rossby wave, anomalous mid-tropospheric vertical motions and anomalous precipitation.

The western Indian Ocean has been warming rapidly over recent decades, causing a greater number o... more The western Indian Ocean has been warming rapidly over recent decades, causing a greater number of extreme climatic events. It is therefore of paramount importance to improve our understanding of links between In-dian Ocean sea surface temperature (SST) variability, climate change and sustainability of tropical coral reef ecosystems. Here we present monthly resolved coral Sr / Ca records from two different locations from Rodrigues Island (63 • E, 19 • S) in the south-central Indian Ocean trade wind belt. We reconstruct SST based on a linear relationship with the Sr / Ca proxy with records starting from 1781 and 1945, respectively. We assess relationships between the observed long-term SST and climate fluctuations related to the El Niño–Southern Oscillation (ENSO), the Subtropical Indian Ocean Dipole Mode (SIOD) and the Pacific Decadal Oscillation (PDO) between 1945 and 2006, respectively. The reproducibility of the Sr / Ca records is assessed as are the potential impacts of diagenesis and corallite orientation on Sr / Ca–SST reconstructions. We calibrate individual robust Sr / Ca records with in situ SST and various gridded SST products. The results show that the SST record from Cabri provides the first Indian Ocean coral proxy time series that records the SST signature of the PDO in the south-central Indian Ocean since 1945. We suggest that additional records from Rodrigues Island can provide excellent records of SST variations in the southern Indian Ocean trade wind belt to unravel teleconnections with the SIOD/ENSO/PDO on longer timescales.

During the summer of 2010/2011, a regional marine heat wave resulted in coral bleaching of variab... more During the summer of 2010/2011, a regional marine heat wave resulted in coral bleaching of variable severity along much of the western coastline of Australia. At Ningaloo Reef, a 300 km long fringing reef system and World Heritage site, highly contrasting coral bleaching was observed between two morphologically distinct nearshore reef communities located on either side of the Ningaloo Peninsula: Tantabiddi (20% bleaching) and Bundegi (90% bleaching). For this study, we collected coral cores (Porites sp.) from Tantabiddi and Bundegi reef sites to assess the response of the Sr/Ca temperature proxy and Mg/Ca ratios to the variable levels of thermal stress imposed at these two sites during the 2010/2011 warming event. We found that there was an anomalous increase in Sr/Ca and decrease in Mg/Ca ratios in the Bundegi record that was coincident with the timing of severe coral bleaching at the site, while no significant changes were observed in the Tantabiddi record. We show that the change in the relationship of Sr/Ca and Mg/Ca ratios with temperature at Bundegi during the 2010/2011 event reflects changes in related coral ''vital'' processes during periods of environmental stress. These changes were found to be consistent with a reduction in active transport of Ca 21 to the site of calcification leading to a reduction in calcification rates and reduced Rayleigh fractionation of incorporated trace elements. Plain Language Summary In this paper, we compare coral-core geochemical records (Sr/Ca and Mg/Ca) from two reef sites at Ningaloo Reef, Western Australia, which showed highly contrasting coral bleaching severities following a regional heat wave during the summer of 2010/11. We show that anomalous increases in Sr/Ca ratios and decreases in Mg/Ca ratios can provide a distinct signature of past thermal stress events making core records useful for understanding the variable impacts of regional ocean warming events within reef ecosystems. Furthermore, by using a novel approach we were able to explain the formation of these anomalies during periods of thermal stress through changes in coral physiological and kinetic processes, which, along with temperature, also effect the incorporation of trace elements in coral skeleton. This is of particular importance as coral core records are heavily relied upon for the understanding of climate change, yet the mechanisms responsible for acute changes in coral trace element ratios during periods of thermal stress have previously not been discussed. We thus hope our work will contribute to the understanding of coral physiology and the development of more robust records of climate change in the future.

Coral reefs are biologically diverse ecosystems threatened with effective collapse under rapid cl... more Coral reefs are biologically diverse ecosystems threatened with effective collapse under rapid climate change, in particular by recent increases in ocean temperatures. Coral bleaching has occurred during major El Niño warming events, at times leading to the die-off of entire coral reefs. Here we present records of stable isotopic composition, Sr/Ca ratios and extension rate (1940–2004) in coral aragonite from a northern Venezuelan site, where reefs were strongly impacted by bleaching following the 1997–98 El Niño. We assess the impact of past warming events on coral extension rates and geochemical proxies. A marked decrease in coral (Pseudodiploria strigosa) extension rates coincides with a baseline shift to more negative values in oxygen and carbon isotopic composition after 1997–98, while a neighboring coral (Siderastrea siderea) recovered to pre-bleaching extension rates simultaneously. However, other stressors, besides high temperature, might also have influenced coral physiology and geochemistry. Coastal Venezuelan reefs were exposed to a series of extreme environmental fluctuations since the mid-1990s, i.e. upwelling, extreme rainfall and sediment input from landslides. This work provides important new data on the potential impacts of multiple regional stress events on coral isotopic compositions and raises questions about the long-term influence on coral-based paleoclimate reconstructions. Under projected anthropogenic climate change scenarios the widespread destruction of tropical coral reef ecosystems will become a reality over the next decades 1. Current models forecast an increase in average global surface temperatures of at least 2 °C by 2100 relative to the pre-industrial period and up to 3–4 °C under existing patterns of human activity 2. Around 30–50% of worldwide coral reefs have been largely or completely degraded due to the combined effects of local factors and global climate change during recent decades 3. Water temperature is one of the most important variables limiting the growth and distribution of reef-building corals 4. Shallow water tropical corals grow within a temperature range of around 18–30 °C 5. Since the early 1980s sea surface temperatures (SSTs) have rapidly increased and tropical corals have experienced large-scale bleaching and mortality events 6. During periods of sustained high temperature, bleaching occurs, a process during which the symbiosis between corals and their photosynthetic microalgae that live within their cells breaks down. Subsequently, the loss of the symbiotic algae causes whitening (" bleaching ") of the coral tissue 7,8 and leads to their starvation, and in many cases to disease and mortality. For example, in 1998, following a super El Niño high temperature event, widespread coral bleaching and mortality was observed and approximately 16% of the worldwide coral communities bleached and died 8. Climate-induced coral bleaching is one of the most serious threats to present-day coral reefs 9. The Caribbean was heavily impacted by El Niño-related bleaching events in 1995, 1997/98, 2005 10 and 2010. Simultaneously, coastal Venezuelan reefs and marine communities were exposed to a series of extreme

Episodic anomalously warm sea surface temperature (SST) extremes, or marine heatwaves (MHWs), amp... more Episodic anomalously warm sea surface temperature (SST) extremes, or marine heatwaves (MHWs), amplify ocean warming effects and may lead to severe impacts on marine ecosystems. MHW-induced coral bleaching events have been observed frequently in recent decades in the southeast Indian Ocean (SEIO), a region traditionally regarded to have resilience to global warming. In this study, we assess the contribution of El Niño-Southern Oscillation (ENSO) to MHWs across the mostly understudied reefs in the SEIO. We find that in extended summer months, the MHWs at tropical and subtropical reefs (divided at ~20°S) are driven by opposite ENSO polarities: MHWs are more likely to occur at the tropical reefs during eastern Pacific El Niño, driven by enhanced solar radiation and weaker Australian Monsoon, some likely alleviated by positive Indian Ocean Dipole events, and at the subtropical reefs during central Pacific La Niña, mainly caused by increased horizontal heat transport, and in some cases reinforced by local air-sea interactions. Madden-Julian Oscillations (MJO) also modulate the MHW occurrences. Projected future increases in ENSO and MJO intensity with greenhouse warming will enhance thermal stress across the SEIO. Implementing forecasting systems of MHWs can be used to anticipate future coral bleaching patterns and prepare management responses.

GKSS School of Environmental Research, 2004

... available within KIHZ KIHZ-Consortium: J. Zinke 1 , H. von Storch 2 , B. Müller 2 , E. Zorita... more ... available within KIHZ KIHZ-Consortium: J. Zinke 1 , H. von Storch 2 , B. Müller 2 , E. Zorita 2 , B. Rein 3 , H. B. Mieding 4 , H. Miller 4 , A. Lücke 5 , GH Schleser 5 , MJ Schwab 6 , JFW Negendank 6 , U. Kienel 6 ,JF González -Ruoco 8 , Christian Dullo 1 , Anton Eisenhauer 1 ...

Geochemistry, Geophysics, Geosystems, 2011

Many marine fishes have life history strategies that involve ontogenetic changes in the use of co... more Many marine fishes have life history strategies that involve ontogenetic changes in the use of coastal habitats. Such ontogenetic shifts may place these species at particular risk from climate change, because the successive environments they inhabit can differ in the type, frequency and severity of changes related to global warming. We used a dendrochronology approach to examine the physical and biological drivers of growth of adult and juvenile mangrove jack (Lutjanus argentimaculatus) from tropical north-western Australia. Juveniles of this species inhabit estuarine environments and adults reside on coastal reefs. The Niño-4 index, a measure of the status of the El Niño-Southern Oscillation (ENSO) had the highest correlation with adult growth chronologies, with La Niña years (characterised by warmer temperatures and lower salinities) having positive impacts on growth. Atmospheric and oceanographic phenomena operating at ocean-basin scales seem to be important correlates of the processes driving growth in local coastal habitats. Conversely, terrestrial factors influencing precipitation and river runoff were positively correlated with the growth of juveniles in estuaries. Our results show that the impacts of climate change on these two life history stages are likely to be different, with implications for resilience and management of populations.

We report fossil coral records from the Sey- chelles comprising individual time slices of 14–20 s... more We report fossil coral records from the Sey- chelles comprising individual time slices of 14–20 sclero- chronological years between 2 and 6.2kyr BP to reconstruct changes in the seasonal cycle of western Indian Ocean sea surface temperature (SST) compared to the present (1990–2003). These reconstructions allowed us to link changes in the SST bimodality to orbital changes, which were causing a reorganization of the seasonal inso- lation pattern. Our results reveal the lowest seasonal SST range in the Mid-Holocene (6.2–5.2 kyr BP) and around kyr BP, while the highest range is observed around 4.6 kyr BP and between 1990 and 2003. The season of maximum temperature shifts from austral spring (Septem- ber to November) to austral autumn (March to May), fol- lowing changes in seasonal insolation over the past 6 kyr. However, the changes in SST bimodality do not linearly follow the insolation seasonality. For example, the 5.2 and 6.2 kyr BP corals show only subtle SST differences in austral spring and autumn. We use paleoclimate simula- tions of a fully coupled atmosphere–ocean general circu- lation model to compare with proxy data for the Mid- Holocene around 6 kyr BP. The model results show that in the Mid-Holocene the austral winter and spring seasons in the western Indian Ocean were warmer while austral summer was cooler. This is qualitatively consistent with the coral data from 6.2 to 5.2 kyr BP, which shows a similar reduction in the seasonal amplitude compared to the present day. However, the pattern of the seasonal SST cycle in the model appears to follow the changes in inso- lation more directly than indicated by the corals. Our results highlight the importance of ocean–atmosphere interactions for Indian Ocean SST seasonality throughout the Holocene. In order to understand Holocene climate variability in the countries surrounding the Indian Ocean, we need a much more comprehensive analysis of season- ally resolved archives from the tropical Indian Ocean. Insolation data alone only provides an incomplete picture.

A wide range of sea surface temperature (SST) expressions have been observed during the El Niño–S... more A wide range of sea surface temperature (SST) expressions have been observed during the El Niño–South- ern Oscillation events of 1950–2010, which have occurred simultaneously with different global atmospheric circu- lations. This study examines the atmospheric circulation and precipitation during December–March 1950–2010 over the African Continent south of 15 S, a region hereaf- ter known as Southern Africa, associated with eight tropi- cal Pacific SST expressions characteristic of El Niño and La Niña events. The self-organizing map method along with a statistical distinguishability test was used to isolate the SST expressions of El Niño and La Niña. The seasonal precipitation forcing over Southern Africa associated with the eight SST expressions was investigated in terms of the horizontal winds, moisture budget and vertical motion. El Niño events, with warm SST across the east and cen- tral Pacific Ocean and warmer than average SST over the Indian Ocean, are associated with precipitation reductions over Southern Africa. The regional precipitation reduc- tions are forced primarily by large-scale mid-tropospheric subsidence associated with anticyclonic circulation in the upper troposphere. El Niño events with cooler than average SST over the Indian Ocean are associated with precipita- tion increases over Southern Africa associated with lower tropospheric cyclonic circulation and mid-tropospheric ascent. La Niña events, with cool SST anomalies over the central Pacific and warm SST over the west Pacific and Indian Ocean, are associated with precipitation increases over Southern Africa. The regional precipitation increases are forced primarily by lower tropospheric cyclonic circula- tion, resulting in mid-tropospheric ascent and an increased flux of moisture into the region.

Paleoclimate reconstructions based on reef corals require precise detection of diagenetic alterat... more Paleoclimate reconstructions based on reef corals require precise detection of diagenetic alteration. Secondary calcite can significantly affect paleotemperature reconstructions at very low amounts of 􏰀1%. X-ray powder diffraction is routinely used to detect diagenetic calcite in aragonitic corals. This procedure has its limitations as single powder samples might not represent the entire coral heterogeneity. A conventional and a 2-D X-ray diffractometer were calibrated with gravimetric powder standards of high and low magnesium calcite (0.3% to 25% calcite). Calcite contents <1% can be recognized with both diffractometer setups based on the peak area of the calcite [104] reflection. An advantage of 2-D-XRD over convenient 1-D-XRD methods is the nondestructive and rapid detection of calcite with relatively high spatial resolution directly on coral slabs. The calcite detection performance of the 2-D-XRD setup was tested on thin sections from fossil Porites sp. samples that, based on powder XRD measurements, showed <1% calcite. Quantification of calcite contents for these thin sections based on 2-D-XRD and digital image analysis showed very similar results. This enables spot measurements with diameters of 􏰀4 mm, as well as systematic line scans along potential tracks previous to geochemical proxy sampling. In this way, areas affected by diagenetic calcite can be avoided and alternative sam- pling tracks can be defined. Alternatively, individual sampling positions that show dubious proxy results can later be checked for the presence of calcite. The presented calibration and quantification method can be transferred to any 2-D X-ray diffractometer.

Increasing intensity of marine heatwaves has caused widespread mass coral bleaching events, threa... more Increasing intensity of marine heatwaves has caused widespread mass coral bleaching events, threatening the integrity and functional diversity of coral reefs. Here we demonstrate the role of inter-ocean coupling in amplifying thermal stress on reefs in the poorly studied southeast Indian Ocean (SEIO), through a robust 215-year (1795–2010) geochemical coral proxy sea surface temperature (SST) record. We show that marine heatwaves affecting the SEIO are linked to the behaviour of the Western Pacific Warm Pool on decadal to centennial timescales, and are most pronounced when an anomalously strong zonal SST gradient between the western and central Pacific co-occurs with strong La Nin ̃a’s. This SST gradient forces large-scale changes in heat flux that exacerbate SEIO heatwaves. Better understanding of the zonal SST gradient in the Western Pacific is expected to improve projections of the frequency of extreme SEIO heatwaves and their ecological impacts on the important coral reef ecosystems off Western Australia.

Computer Methods in Biomechanics and Biomedical Engineering, 2011