Seasonal characteristics of the Indian Ocean Dipole during the Holocene epoch

Zonal control on Holocene precipitation in northwestern Madagascar based on a stalagmite from Anjohibe

The Malagasy Summer Monsoon is an important part of the larger Indian Ocean and tropical monsoon region. As the effects of global warming play out, changes to precipitation in Madagascar will have important ramifications for the Malagasy people. To help understand how precipitation responds to climate changes we present a long-term Holocene speleothem record from Anjohibe, part of the Andranoboka cave system in northwestern Madagascar. To date, it is the most complete Holocene record from this region and sheds light on the nature of millennial and centennial precipitation changes in this region. We find that over the Holocene, precipitation in northwestern Madagascar is actually in phase with the Northern Hemisphere Asian monsoon on multi-millennial scales, but that during some shorter centennial-scale events such as the 8.2 ka event, Anjohibe exhibits an antiphase precipitation signal to the Northern Hemisphere. The ultimate driver of precipitation changes across the Holocene does not appear to be the meridional migration of the monsoon. Instead, zonal sea surface temperature gradients in the Indian Ocean seem to play a primary role in precipitation changes in northwestern Madagascar.

The strength, position, and width changes of the intertropical convergence zone since the Last Glacial Maximum

The intertropical convergence zone (ITCZ) plays a key role in regulating tropical hydroclimate and global water cycle through changes in its convection strength, latitudinal position, and width. The long-term variability of the ITCZ, along with the corresponding driving mechanisms, however, remains obscure, mainly because it is difficult to separate different ITCZ variables in paleoclimate proxy records. Here, we report a speleothem oxygen isotope (δ18O) record from southwestern Sulawesi, Indonesia, and compile it with other speleothem records from the Maritime Continent. Using the spatial gradient of speleothem δ18O along a transect across the ITCZ, we constrain ITCZ variabilities over the Maritime Continent during the past 30,000 y. We find that ITCZ convection strength overall intensified from the last glacial period to the Holocene, following changes in climate boundary conditions. The mean position of the regional ITCZ has moved latitudinally no more than 3° in the past 30,000 y, consistent with the deduction from the atmospheric energy framework. However, different from modern observations and model simulations for future warming, the ITCZ appeared narrower during both the late Holocene and most part of the last glacial period, and its expansion occurred during Heinrich stadials and the early-to-mid Holocene. We also find that during the last glacial and deglacial period, prominent millennial-scale ITCZ changes were closely tied to the variability of the Atlantic meridional overturning circulation (AMOC), whereas during the Holocene, they were predominantly modulated by the long-term variability of the Walker circulation.

Interannual variation and sources identification of heavy metals in seawater near shipping lanes: Evidence from a coral record from the northern South China Sea

Heavy metal pollution is a serious environmental problem in the marine ecosystem. Thereinto, marine transportation activities have gradually become an important source of heavy metals in seawater. However, the lack of studies on the temporal dynamics of seawater heavy metals in marine shipping areas has hindered our understanding of the sources and transport mechanisms of heavy metals in seawater of hectic shipping waters. Therefore, we investigated the interannual resolution variation of heavy metals in Porites lutea skeletons during the past 32 years under the rapid development of the shipping sector near Weizhou Island from the northern South China Sea. Results show that most heavy metal concentrations with higher coefficients of variation (≥100 %) in the Porites coral skeletons were higher than those in the uncontaminated or less anthropogenic waters. The results of principal component analysis and multiple linear regression showed that the interannual variations of Ni, V, Cr, Co, Zn, Cu, Mn, Fe and Mo were mainly impacted by marine oil extraction and oil spills generated by shipping activities, accounting for 51.58 %. The effect of sea surface temperature accounts for 13.44 %, and controls the interannual variations of Ba and Sr. The effect of industrial pollution accounts for 13.27 %, and explains the interannual variations of Cd and Y. The fuel consumption of marine shipping accounted for 8.76 %, explaining the interannual variations of Pb. The total contribution of anthropogenic activities reached 73.61 %. The interannual variation of heavy metals indicates that hectic marine shipping activities are the dominant cause of Ni, V, Pb, Cr, Co, Zn, Cu, Mn, Fe and Mo input to surface seawater around Weizhou Island. This provided valuable data for understanding the temporal dynamics and potential sources of heavy metals in the marine environment by using coral skeletons as a high-resolution recording vehicle.

Coral Sr/Ca records provide realistic representation of eastern Indian Ocean cooling during extreme positive Indian Ocean Dipole events

Extreme positive Indian Ocean Dipole (pIOD) events are amplified by non-linear ocean–atmosphere interactions and are characterized by pronounced cooling in the eastern equatorial Indian Ocean. These non-linear feedbacks are not adequately represented in historical products of sea surface temperatures that underestimate the magnitude of extreme pIOD events. Here, we present a sea surface temperature (SST) reconstruction based on monthly coral Sr/Ca ratios measured in two coral cores from Enggano Island (Indonesia), that lies in the eastern pole of the IOD. The coral SST reconstruction extends from 1930 to 2008 and captures the magnitude of cooling during extreme pIOD events as shown in recent satellite and reanalysis data of SST that include ocean dynamics. The corals indicate that the 1961 pIOD event was at least as severe as the 1997 event, while the 1963 pIOD was more comparable to the 2006 event. The magnitude 1967 pIOD is difficult to assess at present due to poor replication between coral cores, and may be comparable to either 1997 or 2006. Cooling during the 1972 pIOD was short-lived and followed by pronounced warming, as seen in the moderate pIOD event of 1982. A combination of coral SST reconstructions and an extension of new reanalysis products of SST to historical time scales could help to better assess the severity and impact of past pIOD events such as the ones seen in the 1960s.

Influence of normal tide and the Great Tsunami as recorded through hourly-resolution micro-analysis of a mussel shell

We report here hourly variations of Mg/Ca, Sr/Ca, and Ba/Ca ratios in a Mediterranean mussel shell (Mytilus galloprovincialis) collected at the Otsuchi bay, on the Pacific coast of northeastern Japan. This bivalve was living in the intertidal zone, where such organisms are known to form a daily or bidaily growth line comprised of abundant organic matter. Mg/Ca ratios of the inner surface of the outer shell layer, corresponding to the most recent date, show cyclic changes at 25-90 μm intervals, while no interpretable variations are observed in Sr/Ca and Ba/Ca ratios. High Mg/Ca ratios were probably established by (1) cessation of the external supply of Ca and organic layer forming when the shell is closed at low tide, and (2) the strong binding of Mg to the organic layer, but not of Sr and Ba. Immediately following the great tsunami induced by the 2011 Tohoku earthquake, Mg/Ca enrichment occurred, up to 10 times that of normal low tide, while apparent Ba/Ca enrichment was observed for only a few days following the event, therefore serving a proxy of the past tsunami. Following the tsunami, periodic peaks and troughs in Mg/Ca continued, perhaps due to a biological memory effect as an endogenous clock.

Modern and sub-fossil corals suggest reduced temperature variability in the eastern pole of the Indian Ocean Dipole during the medieval climate anomaly

We present two 40 year records of monthly coral Sr/Ca ratios from the eastern pole of the Indian Ocean Dipole. A modern coral covers the period from 1968 to 2007. A sub-fossil coral derives from the medieval climate anomaly (MCA) and spans 1100-1140 AD. The modern coral records SST variability in the eastern pole of the Indian Ocean Dipole. A strong correlation is also found between coral Sr/Ca and the IOD index. The correlation with ENSO is asymmetric: the coral shows a moderate correlation with El Niño and a weak correlation with La Niña. The modern coral shows large interannual variability. Extreme IOD events cause cooling > 3 °C (1994, 1997) or ~ 2 °C (2006). In total, the modern coral indicates 32 warm/cool events, with 16 cool and 16 warm events. The MCA coral shows 24 warm/cool events, with 14 cool and 10 warm events. Only one cool event could be comparable to the positive Indian Ocean Dipole in 2006. The seasonal cycle of the MCA coral is reduced (< 50% of to the modern) and the skewness of the Sr/Ca data is lower. This suggests a deeper thermocline in the eastern Indian Ocean associated with a La Niña-like mean state in the Indo-Pacific during the MCA.

In situ Mg isotope measurements of biogenic carbonates using laser ablation multi-collector inductively coupled plasma mass spectrometry: A new tool to understand biomineralisation

RATIONALE

Magnesium is one of the most abundant elements in the earth's crust and in seawater. Fractionation of its stable isotopes has been shown to be a useful indicator of many geological, chemical, and biological processes. For example, biogenic carbonates display an ~5‰ range of δ²⁶ Mg values, which is attributed to variable degrees of biological control on Mg ions during biomineralisation. Understanding this biological control is essential for developing proxies based on biogenic carbonates.

METHODS

In this work, we present a new approach of measuring Mg isotopes in biogenic carbonates using Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICPMS).

RESULTS

Our results show that this microanalytical approach provides relatively fast, high spatial resolution (<0.2 μm) measurements with high precision and accuracy down to 0.2‰ (2SE). To achieve high levels of precision and accuracy, baseline interferences need to be monitored and a carbonate standard with a relatively low trace metal composition similar to biogenic carbonates should be used. We also demonstrate that the matrix effect on Mg isotopes in carbonates with low Fe and Mn is limited to less than 0.2‰ fractionation under different laser parameters and low oxide condition (<0.3% ThO/Th).

CONCLUSIONS

Our newly developed LA-MC-ICPMS method and its applications to biogenic carbonates show significant advantages provided by the microanalytical approach in understanding complex processes of biomineralisation in marine calcifiers.

Coupling of Indo-Pacific climate variability over the last millennium

The Indian Ocean Dipole (IOD) affects climate and rainfall across the world, and most severely in nations surrounding the Indian Ocean^1-4. The frequency and intensity of positive IOD events increased during the twentieth century⁵ and may continue to intensify in a warming world⁶. However, confidence in predictions of future IOD change is limited by known biases in IOD models⁷ and the lack of information on natural IOD variability before anthropogenic climate change. Here we use precisely dated and highly resolved coral records from the eastern equatorial Indian Ocean, where the signature of IOD variability is strong and unambiguous, to produce a semi-continuous reconstruction of IOD variability that covers five centuries of the last millennium. Our reconstruction demonstrates that extreme positive IOD events were rare before 1960. However, the most extreme event on record (1997) is not unprecedented, because at least one event that was approximately 27 to 42 per cent larger occurred naturally during the seventeenth century. We further show that a persistent, tight coupling existed between the variability of the IOD and the El Niño/Southern Oscillation during the last millennium. Indo-Pacific coupling was characterized by weak interannual variability before approximately 1590, which probably altered teleconnection patterns, and by anomalously strong variability during the seventeenth century, which was associated with societal upheaval in tropical Asia. A tendency towards clustering of positive IOD events is evident in our reconstruction, which-together with the identification of extreme IOD variability and persistent tropical Indo-Pacific climate coupling-may have implications for improving seasonal and decadal predictions and managing the climate risks of future IOD variability.

Coherent response of the Indian Monsoon Rainfall to Atlantic Multi-decadal Variability over the last 2000 years

Indian Summer Monsoon (ISM) rainfall has a direct effect on the livelihoods of two billion people in the Indian-subcontinent. Yet, our understanding of the drivers of multi-decadal variability of the ISM is far from being complete. In this context, large-scale forcing of ISM rainfall variability with multi-decadal resolution over the last two millennia is investigated using new records of sea surface salinity (δ18Ow) and sea surface temperatures (SSTs) from the Bay of Bengal (BoB). Higher δ18Ow values during the Dark Age Cold Period (1550 to 1250 years BP) and the Little Ice Age (700 to 200 years BP) are suggestive of reduced ISM rainfall, whereas lower δ18Ow values during the Medieval Warm Period (1200 to 800 years BP) and the major portion of the Roman Warm Period (1950 to 1550 years BP) indicate a wetter ISM. This variability in ISM rainfall appears to be modulated by the Atlantic Multi-decadal Oscillation (AMO) via changes in large-scale thermal contrast between the Asian land mass and the Indian Ocean, a relationship that is also identifiable in the observational data of the last century. Therefore, we suggest that inter-hemispheric scale interactions between such extra tropical forcing mechanisms and global warming are likely to be influential in determining future trends in ISM rainfall.

The turnover of continental planktonic diatoms near the middle/late Miocene boundary and their Cenozoic evolution

Fossil evidence indicates that modern assemblages of temperate nonmarine planktonic diatoms began near the middle/late Miocene boundary when the genus Actinocyclus, an important constituent of lacustrine planktonic diatom assemblages during the early to middle Miocene, was replaced by genera of the family Stephanodiscaceae. This floral turnover has been confirmed in many regions of the world, except eastern Asia where taxonomic data about early and middle Miocene planktonic diatom assemblages have until recently been scarce. Our analysis of Lower and Middle Miocene lacustrine diatomaceous rocks in Japan confirms that species of nonmarine Actinocyclus were important constituents of lake phytoplankton there as well. The appearance of nonmarine Actinocyclus species near the beginning of the Miocene may have resulted from the introduction of euryhaline species into lacustrine environments during a highstand of sea level at that time. Similarly, it is possible that species of Stephanodiscaceae evolved from marine thalassiosiroid ancestors that invaded high latitude lacustrine environments during multiple Paleogene highstands, resulting in a polyphyletic origin of the family. The turnover from nonmarine Actinocyclus to Stephanodiscaceae genera near the middle/late Miocene boundary may be linked to a contemporaneous increase in silica concentrations in lakes caused by active volcanism, increased weathering of silicate rocks due to orogeny, and the expansion of C4 grasslands. This turnover may also have been influenced by enhanced seasonal environmental changes in the euphotic zone caused by the initiation of monsoon conditions and a worldwide increase in meridional temperature gradients during the late Miocene. Morphological characteristics of Stephanodiscaceae genera, such as strutted processes and small size, suggest their species were better adapted to seasonal environmental changes than nonmarine species of Actinocyclus because of their superiority in floating and drifting capabilities and possibly metabolism, intrinsic growth rate, and reproductivity. As climates deteriorated during the late Miocene, Stephanodiscaceae species may have spread from high latitudes to temperate lakes where they diversified, ultimately displacing Actinocyclus.

Coral Sr/Ca-based sea surface temperature and air temperature variability from the inshore and offshore corals in the Seribu Islands, Indonesia

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.

Meteorological influences on dengue transmission in Pakistan

OBJECTIVE

To identify the influences of local and regional climate phenomena on dengue transmission in Lahore District of Pakistan, from 2006 to 2014.

METHODS

Time-series models were applied to analyze associations between reported cases of dengue and climatic parameters. The coherence trend of regional climate phenomena (IOD and ENSO) was evaluated with wavelet analysis.

RESULTS

The minimum temperature 4 months before the dengue outbreak played the most important role in the Lahore District (P = 0.03). A NINO 3.4 index 9 months before the outbreaks exhibited a significant negative effect on dengue transmission (P = 0.02). The IOD exhibited a synchronized pattern with dengue outbreak from 2010 to 2012. The ENSO effect (NINO 3.4 index) might have played a more important role after 2012.

CONCLUSIONS

This study provides preliminary results of climate influences on dengue transmission in the Lahore District of Pakistan. An increasing dengue transmission risk accompanied by frequent climate changes should be noted. Integrating the influences of climate variability into disease prevention strategies should be considered by public health authorities.

A Regional Stable Carbon Isotope Dendro-Climatology from the South African Summer Rainfall Area

Carbon isotope analysis of four baobab (Adansonia digitata L.) trees from the Pafuri region of South Africa yielded a 1000-year proxy rainfall record. The Pafuri record age model was based on 17 radiocarbon dates, cross correlation of the climate record, and ring structures that were presumed to be annual for two of the trees. Here we present the analysis of five additional baobabs from the Mapungubwe region, approximately 200km west of Pafuri. The Mapungubwe chronology demonstrates that ring structures are not necessarily annually formed, and accordingly the Pafuri chronology is revised. Changes in intrinsic water-use efficiency indicate an active response by the trees to elevated atmospheric CO2, but this has little effect on the environmental signal. The revised Pafuri record, and the new Mapungubwe record correlate significantly with local rainfall. Both records confirm that the Medieval Warm Period was substantially wetter than present, and the Little Ice Age was the driest period in the last 1000 years. Although Mapungubwe is generally drier than Pafuri, both regions experience elevated rainfall peaking between AD 1570 and AD 1620 after which dry conditions persist in the Mapungubwe area until about AD 1840. Differences between the two records correlate with Agulhas Current sea-surface temperature variations suggesting east/west displacement of the temperate tropical trough system as an underlying mechanism. The Pafuri and Mapungubwe records are combined to provide a regional climate proxy record for the northern summer rainfall area of southern Africa.

A Regional Stable Carbon Isotope Dendro-Climatology from the South African Summer Rainfall Area

Carbon isotope analysis of four baobab (Adansonia digitata L.) trees from the Pafuri region of South Africa yielded a 1000-year proxy rainfall record. The Pafuri record age model was based on 17 radiocarbon dates, cross correlation of the climate record, and ring structures that were presumed to be annual for two of the trees. Here we present the analysis of five additional baobabs from the Mapungubwe region, approximately 200km west of Pafuri. The Mapungubwe chronology demonstrates that ring structures are not necessarily annually formed, and accordingly the Pafuri chronology is revised. Changes in intrinsic water-use efficiency indicate an active response by the trees to elevated atmospheric CO₂, but this has little effect on the environmental signal. The revised Pafuri record, and the new Mapungubwe record correlate significantly with local rainfall. Both records confirm that the Medieval Warm Period was substantially wetter than present, and the Little Ice Age was the driest period in the last 1000 years. Although Mapungubwe is generally drier than Pafuri, both regions experience elevated rainfall peaking between AD 1570 and AD 1620 after which dry conditions persist in the Mapungubwe area until about AD 1840. Differences between the two records correlate with Agulhas Current sea-surface temperature variations suggesting east/west displacement of the temperate tropical trough system as an underlying mechanism. The Pafuri and Mapungubwe records are combined to provide a regional climate proxy record for the northern summer rainfall area of southern Africa.

A 1000-Year Carbon Isotope Rainfall Proxy Record from South African Baobab Trees (Adansonia digitata L.)

A proxy rainfall record for northeastern South Africa based on carbon isotope analysis of four baobab (Adansonia digitata L.) trees shows centennial and decadal scale variability over the last 1,000 years. The record is in good agreement with a 200-year tree ring record from Zimbabwe, and it indicates the existence of a rainfall dipole between the summer and winter rainfall areas of South Africa. The wettest period was c. AD 1075 in the Medieval Warm Period, and the driest periods were c. AD 1635, c. AD 1695 and c. AD1805 during the Little Ice Age. Decadal-scale variability suggests that the rainfall forcing mechanisms are a complex interaction between proximal and distal factors. Periods of higher rainfall are significantly associated with lower sea-surface temperatures in the Agulhas Current core region and a negative Dipole Moment Index in the Indian Ocean. The correlation between rainfall and the El Niño/Southern Oscillation Index is non-static. Wetter conditions are associated with predominantly El Niño conditions over most of the record, but since about AD 1970 this relationship inverted and wet conditions are currently associated with la Nina conditions. The effect of both proximal and distal oceanic influences are insufficient to explain the rainfall regime shift between the Medieval Warm Period and the Little Ice Age, and the evidence suggests that this was the result of a northward shift of the subtropical westerlies rather than a southward shift of the Intertropical Convergence Zone.

Middle Holocene daily light cycle reconstructed from the strontium/calcium ratios of a fossil giant clam shell

Insolation is an important component of meteorological data because solar energy is the primary and direct driver of weather and climate. Previous analyses of cultivated giant clam shells revealed diurnal variation in the Sr/Ca ratio, which might reflect the influence of the daily light cycle. We applied proxy method to sample from prehistoric era, a fossil giant clam shell collected at Ishigaki Island in southern Japan. The specimen was alive during the middle Holocene and thus exposed to the warmest climate after the last glacial period. This bivalve species is known to form a growth line each day, as confirmed by the analysis of the Sr enrichment bands using EPMA and facilitated age-model. We analyzed the Sr/Ca, Mg/Ca and Ba/Ca ratios along the growth axis, measuring a 2-μm spot size at 2-μm interval using NanoSIMS. The Sr/Ca ratios in the winter layers are characterized by a striking diurnal cycle consisting of narrow growth lines with high Sr/Ca ratios and broad growth bands with low Sr/Ca ratios. These variations, which are consistent with those of the cultivated clam shell, indicate the potential for the reconstruction of the variation in solar insolation during the middle Holocene at a multi-hourly resolution.

Hydroclimate of the western Indo-Pacific Warm Pool during the past 24,000 years

The Indo-Pacific Warm Pool (IPWP) is a key site for the global hydrologic cycle, and modern observations indicate that both the Indian Ocean Zonal Mode (IOZM) and the El Niño Southern Oscillation exert strong influence on its regional hydrologic characteristics. Detailed insight into the natural range of IPWP dynamics and underlying climate mechanisms is, however, limited by the spatial and temporal coverage of climate data. In particular, long-term (multimillennial) precipitation patterns of the western IPWP, a key location for IOZM dynamics, are poorly understood. To help rectify this, we have reconstructed rainfall changes over Northwest Sumatra (western IPWP, Indian Ocean) throughout the past 24,000 y based on the stable hydrogen and carbon isotopic compositions (δD and δ(13)C, respectively) of terrestrial plant waxes. As a general feature of western IPWP hydrology, our data suggest similar rainfall amounts during the Last Glacial Maximum and the Holocene, contradicting previous claims that precipitation increased across the IPWP in response to deglacial changes in sea level and/or the position of the Intertropical Convergence Zone. We attribute this discrepancy to regional differences in topography and different responses to glacioeustatically forced changes in coastline position within the continental IPWP. During the Holocene, our data indicate considerable variations in rainfall amount. Comparison of our isotope time series to paleoclimate records from the Indian Ocean realm reveals previously unrecognized fluctuations of the Indian Ocean precipitation dipole during the Holocene, indicating that oscillations of the IOZM mean state have been a constituent of western IPWP rainfall over the past ten thousand years.

Past daily light cycle recorded in the strontium/calcium ratios of giant clam shells

The historical record of daily light cycle in tropical and subtropical regions is short. Moreover, it remains difficult to extract this cycle in the past from natural archives such as biogenic marine carbonates. Here we describe the precise analysis of Sr/Ca, Mg/Ca, and Ba/Ca ratios in a cultivated giant clam shell, using a laterally high-resolution secondary ion mass spectrometer with 2 μm resolution. The Sr/Ca ratio exhibits striking diurnal variations, reflecting the daily light cycle. A clear seasonal variation in Sr/Ca is also observed in another longer set of measurements with 50 μm resolution. Light-enhanced calcification and elemental transportation processes, in giant clam and symbiotic algae, may explain these diurnal and annual variations. This opens the possibility to develop the Sr/Ca ratio from a giant clam shell as an effective proxy for parameters of the daily light cycle.

Two staged pattern formation and spontaneous wave breakup in the ferroin-bromate-pyrocatechol reaction

This report investigated nonlinear spatiotemporal behavior in the ferroin-bromate-pyrocatechol reaction, in which two stages of wave formation, separated by several hours of quiescent period, were observed. In addition to its great photosensitivity, the second stage wave activity could undergo spontaneous breakups at broad reaction conditions. Analysis based on one-dimensional space-time plot suggests that the breakup was caused by propagation slowdown of the leading wave. Due to the presence of coupled autocatalytic reactions, the propagation of the initial and the second stage waves exhibited different and subtle responses to the variation of the concentration of each reagent.

Gas production in the bromate-pyrocatechol oscillator

A significant amount of gas production has been observed in the bromate-pyrocatechol oscillator under high concentrations of bromate and pyrocatechol. The observation is in contrast to the general perception that aromatic compounds can form bromate-based oscillators that are free of gas bubbles, which is a desired property in investigating pattern formation. Analysis with (1)H NMR, (13)C NMR, mass spectrometry, and X-ray crystallography illustrate the production of 5-(dibromomethylene)-2(5H)-furanone from pyrocatechol, where the loss of one carbon atom from the aromatic ring causes the formation of gas bubbles. Possible mechanisms have been proposed to explain the observed phenomenon.

Northern hemisphere controls on tropical southeast African climate during the past 60,000 years

The processes that control climate in the tropics are poorly understood. We applied compound-specific hydrogen isotopes (deltaD) and the TEX(86) (tetraether index of 86 carbon atoms) temperature proxy to sediment cores from Lake Tanganyika to independently reconstruct precipitation and temperature variations during the past 60,000 years. Tanganyika temperatures follow Northern Hemisphere insolation and indicate that warming in tropical southeast Africa during the last glacial termination began to increase approximately 3000 years before atmospheric carbon dioxide concentrations. deltaD data show that this region experienced abrupt changes in hydrology coeval with orbital and millennial-scale events recorded in Northern Hemisphere monsoonal climate records. This implies that precipitation in tropical southeast Africa is more strongly controlled by changes in Indian Ocean sea surface temperatures and the winter Indian monsoon than by migration of the Intertropical Convergence Zone.