Sea Level Variations Research Articles

Examining the performance of along-track multi-mission satellite altimetry – A case study for Sentinel-6

Abstract Satellite altimetry (SA) is one of the most valuable techniques that measure the sea level data at both the near-coast and offshore. There exists, however, multiple challenges and hindrances in determining and using accurate sea level data. The most pertinent is that evaluation of SA performance requires that all data sources (such as tide gauges (TG) and hydrodynamic models (HDMs)) refer to the same vertical datum. Thus, knowledge of the geoid (equipotential surface of the earth) is essential in linking different sources of sea level. Accordingly, this study examines performance of along-track data for three satellite missions (Sentinel-3A, Jason-3, and Sentinel-6A) to obtain realistic sea level variation and to determine the accuracy of the various missions in the complex area of the eastern Baltic Sea. The methodology consisted of utilizing SA, HDM, and TG data and a high-resolution geoid model. Results show that root-mean-square error (RMSE) varied for Jason-3 within a range of 1.68–50.14 cm, Sentinel 3A with a range of 2.8–46.27 cm, and Sentinel 6A with a range of 3.5–43.90 cm. Sentinel 6A was determined to be the most accurate and reliable satellite mission. Results also showed higher RMSE (15.7–46.2 cm) during (i) the seasonal sea ice month (e.g. March 2018); (ii) at locations of several islands (e.g. eastern section of Gulf); and (iii) at locations where rivers discharged into the Gulf (e.g. Nava, Kemi, Luga, and Neva rivers). These features tended to show up as peaks in the final results even though robust data processing for outliers were undertaken. These results suggests that improvements can still be made in the SA retrackers and also in the data-processing techniques utilized.

Exploring Variability in Sea Level at a Tide Gauge Station through Control Charts

Monitoring temporal changes in sea level is important in assessing coastal risk. Sea level anomalies at a tide gauge station, if kinematically conceived, include systematic variations such as trend, acceleration, periodic oscillations, and random disturbances. Among them, the non-stationary nature of the random sea level variations of known or unknown origin at coastal regions has been long recognized by the sea level community. This study proposes the analyses of subgroups of random residual statistics of a rigorously formulated kinematic model solution of tide gauge variations using X-bar and S control charts. The approach is demonstrated using Key West, Florida tide gauge records. The mean and standard errors of 5-year-long subgroups of the residuals revealed that sea level changes at this location have been progressively intensifying from 1913 to the present. Increasing oscillations in sea level at this locality may be attributed partly to the thermal expansion of seawater with increasing temperatures causing larger buoyancy-related sea level fluctuations as well as the intensification of atmospheric events including wind patterns and the impact of changes in inverted barometer effects that will alter coastal risk assessments for the future.

Rapid Sea Level Rise in the Tropical Southwest Indian Ocean in the Recent Two Decades

AbstractIt has been reported that the sea level falls in the tropical Southwest Indian Ocean (SWIO) from the 1960s to the early 2000s. However, a rising trend of 4.05 ± 0.56 cm/decade has occurred during the recent two decades with our analysis showing that manometric sea level contributes 41% to this sea level rise. 30% of this rise is due to steric sea level (SSL) change in the upper 2,000 m with SSL rise in the upper 300 m of secondary importance. Conversely, thermal expansion below the thermocline (300–2,000 m), likely caused by water mass spread from the Southern Ocean, induces major contribution to SSL changes. Compared to existing studies demonstrating the contribution of thermal variations above the thermocline to sea level variability in the tropical SWIO, this study emphasizes the importance of ocean mass and deeper ocean changes in a warming climate.

Empirical projection of global sea level in 2050 driven by Antarctic and Greenland ice mass variations

Global mean sea level rise, driven by ice mass loss in Antarctic and Greenland Ice Sheets (AIS and GrIS), is a significant consequence of global warming. Although various ice sheet models have attempted to predict the ice mass balance and subsequent sea level changes, non-trivial disagreements between models exist. In this study, we employ an empirical approach to estimate the future (2050) ice mass changes for both ice sheets, assuming their historical patterns of ice dynamics would persist in the coming decades. To achieve this, we estimate decadal-scale ice discharge variations by subtracting the surface mass balance (SMB) from the observed ice mass changes and extrapolate linear trend and acceleration components of ice discharges up to 2050. We also consider future SMB data from Coupled Model Intercomparison Project phase 6 models to estimate net ice mass balance. Our estimates suggest that from 2021 to 2050, the global sea level rise due to AIS and GrIS ranges between 6–19 mm and 15–31 mm, respectively. Additionally, we investigate regional sea level variability resulting from geoid changes induced by ice mass changes in both regions, highlighting that heterogeneous sea level changes may cause more pronounced sea level rises in lower latitude regions, where major cities are located.

Influence of rossby wave in southern Indian Ocean on the low frequency variability of eddy kinetic energy within agulhas current system

The basin-scale wave propagation in the Southern Indian Ocean (SIO) is inferred to affect the low-frequency variability of eddy kinetic energy (EKE) within the Agulhas current system (ACS). Observations and numerical simulations indicate that westward-propagating waves, in the form of sea level variability from the east boundary, may cause “non-linear” oceanic responses (e.g., sea level and EKE) in the ACS. This is likely due to two factors: (i) the movement of wave crests and troughs continuously alters the stratification of the upper ocean, generating a positive baroclinic instability and prompting conversions of EKE from mean flow in the source regions, and (ii) wave-current interactions induce a rapid intension of an anticyclone gyre in the interior SIO and the corresponding EKE in the downstream regions. These basin-scale wave modulations may provide an additional perspective to the traditional wind driving view based on the barotropic Sverdrup relation. The local winds over the SIO play an important role in maintaining basin-scale Rossby waves in the southwest Indian Ocean and further modulating oceanic low-frequency variability in a “quasi-linear” way.

Virtual coastal altimetry tide gauges along the West African coast

Low-lying coastal regions are generally vulnerable to climate change, and particularly to sea level variations. Understanding how these variations affect the coastal population requires an access to sea level measurements. Good quality in-situ sea level data are seldom available, with most long, research quality data in Europe and North America. In contrast, satellite altimetry provides more than three decades of near-global, continuous and freely available sea level measurements. Thanks to recent advances in processing and instruments, these observations have now become reliable to a few kilometers from the coast. In this study, using the available in-situ tide gauge data as a reference, we explore the ability of the recent X-TRACK/ALES high-resolution coastal altimeter product to derive the ocean tide and the long-term sea level changes along the West African coast. This region was chosen because it is under-sampled in terms of in-situ observations and would benefit greatly from the availability of freely accessible satellite data sets. To select the altimetry observations closest to the coast, we first define virtual tide gauges as close as possible to the intersection between each satellite track and the land. Sea level anomalies derived from the virtual stations were observed to be similar to those from the corresponding tide gauge stations: correlation values are between 0.58 and 0.78, root mean square differences between 5.6 and 8.3 cm. The virtual stations reproduce the observed tide with errors less or equal to 6.5 cm (i.e. 5.8% or less than the sea level variations of the tide). We show that part of the differences in tides between the two datasets is explained by differences in position between tide gauges and virtual stations. The combined analysis of sea level trends derived from tide gauges and from virtual stations shows how it is an efficient strategy to correct their respective errors and progress towards increasingly accurate sea level trend estimates in a region with little or no research-quality tide gauge data suitable for long-term sea level studies. The conclusion from this study is that in coastal regions poorly covered by tide gauges, our altimetry-based approach can be used to study and monitor sea-level variations related to tides or to long-term sea level changes.

Sea level oscillations spectra of a shallow coastal bay: Cost-effective measurements and numerical modelling in Kruglaya Bay

Seiches are long standing waves typical of enclosed and semi-enclosed basins. It is shown that they can be generated in bays by long-period waves coming from open sea through an entry. An interaction between adjacent bays may extend the number of seiche modes in these bays. Kruglaya Bay is widely used for recreational purposes. We measured sea level variations in Kruglaya Bay in August-October, 2022 by means of a cost-effective and robust autonomous sea-level recorder designed and assembled in Marine Hydrophysical Institute. Measurements were conducted based on an ultra-sound JSN-SR04T sensor. SWASH, a numerical high-resolution model, was used to simulate dissipating free oscillations in a system of connected shallow semi-enclosed bays initiated by long waves incoming from the open sea. A spectral analysis of measured sea level fluctuations was used to identify resonant periods of local seiches in Kruglaya Bay. Estimate periods of oscillations that correspond to incoming long waves from the neighbouring bays were obtained using the results of mathematical modeling. The performed wavelet analysis permitted to identify situations when local resonant oscillations were initiated before wind intensification (which manifested as an increase in energy at the high-frequency part of the spectrum). An intense fundamental mode (also known as the ‘Helmholtz mode’ of a semi-enclosed oscillating basin) of Kruglaya Bay (period around 14 min) was identified both in measurements and the numerical simulation. The power spectra of the sea level oscillations in Kruglaya Bay also showed significant peaks at the periods of fundamental modes of the neighbouring bays. Besides, periods of the Black Sea seiches (1.25 h and 2.5 h) were identified from the observations.

Impact of Mass Redistribution on Regional Sea Level Changes Over the South China Sea Shelves

AbstractThis study investigates long‐term sea level changes in the South China Sea (SCS) using a validated high‐resolution regional ocean model simulation for the Maritime Continent. The contributions of ocean mass redistribution and steric sea level are examined to understand the sea level variations. The ocean bottom pressure (OBP) serves as an indicator of sea level variations linked to alterations in ocean mass flux. The OBP accounts for over 80% of the total sea level change over the shelves, while the steric sea level emerges as the dominant factor, contributing over 50% to the sea level change in the deep SCS. Luzon Strait transport shows a weakening trend in the last six decades, resulting in higher heat accumulation and larger steric expansion in the deep SCS. The ocean mass redistribution acts as a mechanism to balance the contrasting steric induced sea level changes over the deep SCS and shallow continental shelves.

Sea level variability and modeling in the Gulf of Guinea using supervised machine learning

The rising sea levels due to climate change are a significant concern, particularly for vulnerable, low-lying coastal regions like the Gulf of Guinea (GoG). To effectively address this issue, it is crucial to gain a comprehensive understanding of historical sea level variability, and the influencing factors, and develop a reliable modeling system for future projections. This knowledge is essential for informed planning and mitigation strategies aimed at protecting coastal communities and ecosystems. This study presents a comprehensive analysis of mean sea level anomaly (MSLA) trends in the GoG between 1993 and 2020, covering three distinct periods (1993–2002, 2003–2012, and 2013–2020). It investigates the connections between interannual sea level variability and large-scale oceanic and atmospheric forcings. Furthermore, the study evaluates the performance of supervised machine learning techniques to optimize sea level modeling. The findings reveal a consistent rise in MSLA linear trends across the basin, particularly pronounced in the northern region, with a total linear trend of 88 mm over the entire period. The highest decadal trend (38.7 mm) emerged during 2013–2020, with the most substantial percentage increment (100%) occurring in 2003–2012. Spatial variation in decadal sea-level trends was influenced by subbasin physical forcings. Strong interannual signals in the spatial sea level distribution were identified, linked to large-scale oceanic and atmospheric phenomena. Seasonal variations in sea level trends are attributed to seasonal changes in the forcing factors. The evaluation of supervised learning modeling methods indicates that Random Forest Regression and Gradient Boosting Machines are the most accurate, reproducing interannual sea level patterns in the GoG with 97% and 96% accuracy. These models could be used to derive regional sea level projections via downscaling of climate models. These findings provide essential insights for effective coastal management and climate adaptation strategies in the GoG.

Sea-level rise in Southeast Asia: a review of the factors, and the observed rates from tide gauge, satellite altimeters and assimilated data techniques

ABSTRACT Sea-level rise (SLR) has become a serious global threat resulting from the climate change. The global rate of SLR observed by the long records of satellite altimeters (1993–2011) is at 3.11 mm/yr with the mean rate at Southeast Asia (SEA) slightly higher at 3.9 mm/yr (1993–2009). Many countries in SEA face the risk of SLR highlighting the flood dangers. In addition to the land prone to sinking, several countries like Indonesia face extreme SLR events. To provide an understanding of the SLR rates in SEA, this paper answers several questions associated with SLR in SEA. What are the factors that contributed to the SLR on regional scales? How can the SLR be mathematically modelled? How much has the sea level increased over the past decades based on the observed tide gauge, radar altimeters and data assimilation techniques? SLR from these techniques is reviewed because they provide the complete spectrum of processes that lead to sea-level variability. Finally, the prospects for future research are summarized in order to provide guidance for the future SLR studies.

ESMGFZ EAM Products for EOP Prediction: Toward the Quantification of Time Variable EAM Forecast Errors

Abstract Since more than 10 years, the Earth system modeling group at GFZ (ESMGFZ) provides effective angular momentum (EAM) functions for Earth orientation parameter assessment on a routinely daily basis. In addition to EAM of the individual Earth’s subsystems atmosphere, ocean, and hydrology, the global mass balance is calculated as barystatic sea level variation by solving explicitly the sea-level equation. ESMGFZ provides also 6-day forecasts for all of these EAM products. EAM forecasts are naturally degraded by forecast errors that typically grow with increasing forecast length, but they also show recurring patterns with occasionally higher errors at very short forecast horizons. To characterize such errors which are not randomly distributed in time, we divided the errors into a systematic and a stochastic contribution. In an earlier study, we were able to detect and remove the large systematic fraction occurring in the atmospheric angular momentum (AAM) wind term forecast errors with a cascading forward neural network model, thereby reducing the total forecast error by about 50%. In contrast, we were not able to remove the random error component assed in this study. Nevertheless, we show that machine learning methods are able to predict quasi-daily variations in time variable EAM forecasts error levels. We plan to provide these forecast error estimates along with the deterministic EAM forecast products for subsequent use in, for example, EOP Kalman filter prediction schemes.

Geochemical and sedimentary features of the unusual association between hybrid carbonates and beachrocks in the Southeastern Brazilian Coast

Rocks formed in beach environments during the Holocene constitute strong evidences of relative sea level variations (RSL) and supply important data for paleoenvironmental reconstruction. At the southeastern Brazilian coast, an unusual association of lithofacies composed of hybrid carbonates and beachrocks was identified on the Parati beach in the Espírito Santo state. In this study, radiocarbon dating and sedimentary and geochemical characterization of five lithofacies were conducted, with the aim of reconstructing the paleoenvironmental conditions of deposition and cementation of this facies association. The lithofacies were classified as quartzarenites, bioclastic quartzarenites, hybrid carbonate and hybrid boundstones, with ages ranging from 2600 to 700 cal yr BP. Sedimentary and geochemical changes observed in these five lithofacies of the shallow shelf off southeastern Brazil reinforce evidence relative sea level variations during the Holocene.

Skillful multiyear to decadal predictions of sea level in the North Atlantic Ocean and U.S. East Coast

Long-term sea-level rise and multiyear to decadal sea level variations pose substantial risks for flooding and erosion in coastal communities. Here we use observations and climate model predictions to show that sea level variations along the U.S. East Coast are skillfully predictable 3 to 10 years in advance. The most predictable component of sea level is a basin scale upward trend, predictable a decade in advance and primarily a response to increasing greenhouse gases. Significant additional predictability comes from multidecadal variations of the Atlantic Meridional Overturning Circulation (AMOC). While perfect model simulations show AMOC-related sea level predictability of 5-7 years, model biases and initialization uncertainties reduce the realized predictive skill to 3-5 years, depending on location. Overall, greenhouse gas warming and predictable AMOC variations lead to multiyear to decadal prediction skill for sea level along the U.S. East Coast. Such skill could have significant societal benefit for planning and adaptation.

Analysis of the Shoreline Changes using Geoinformatics in Ghoramara Island of Hugli Estuary, West Bengal in India

Conceptual FrameworkCoastal decrepitude is the loss of topographical resources along the coast as a result of silt, temperature fluctuations, tidal shifts, and wave breaking. Hydraulic activity, scraping, abrasion, and erosion are the major causes of erosion; other factors that affect it include the condition of the shore, rocks, joints, fissures, marine chemical reactions, and wave force. ObjectivesThe primary objectives of this study are to analyze the coastline changes between 1972 and 2022 utilizing remote sensing and GIS data and forecast the changes in the shoreline in 2032. MethodsThe study examined coastal areas from 1972 to 2022 using multi-temporal satellite data from Landsat TM and Landsat OLI/TIRS. Shoreline change and the calculations related to it were examined using the Digital Shoreline Analysis System using near-infrared bands and tasseled cap transformation, to determine the rate of change in the shoreline, the study also employed Shoreline Change Envelope and End Point Rate techniques. ResultsCoastal erosion caused substantial damage to the island between 1972 and 2022. The northern, southeastern, and western regions of the coast are seeing the highest levels of coastal erosion. The south coast experiences considerable erosion, whereas the west and southeast coasts experience the least. The EPR of Ghoramara Island has mean, minimum, and maximum changes of -10.59, -4.13, and -35.93, respectively. A notable inshore shift has occurred in the northern portion of Ghoramara, extending from 676 meters to 855 meters. The study also uses tidal gauge records and Revised Local Reference data from the Haldia Gauge Station to track long-term sea level variations. According to the study, Ghoramara Island's shoreline will change by 2032, with the greatest negative changes expected to occur around the island's western and southern borders. ConclusionThe study shows a significant decrease in Ghoramara's shoreline regions between 1972 and 2022, with a 3,000-population shifted from the place in 2016 due to Lohachara's submergence. Changes in the island's morphology and human activities have reduced cultivation. The study suggests increasing mangrove vegetation to combat coastal erosion and prevent further displacement of people to neighboring islands.

Aptian major changes in accommodation. New sedimentary evidence from the Maestrat Basin (E Iberia)

Global sea-level fluctuations with amplitudes of tens of metres and durations between 0.5 and 3 Myr are well-known oceanographic events of the Cretaceous Period. During recent years, major Cretaceous changes in accommodation recorded in different basins have been mainly interpreted as eustatically driven. Two episodes of major relative sea-level fall and rise of late early and early late Aptian age were investigated in the Maestrat Basin (E Iberian Peninsula). Previously documented in eight outcrops, these Aptian records of major changes in accommodation have now been identified in five additional localities within the basin, suggesting at least a basin-wide significance of these relative sea-level fluctuations. The records of relative sea-level fall analysed are associated with the local development of incised valleys and forced regressive wedges. Two upper lower Aptian incised valleys, which are downcutting highstand platform carbonates dominated by rudists and corals, were studied and show depths of approximately 10 and 80 m. The incision depths measured indicate amplitudes of relative sea-level variations in the order of tens of metres. During subsequent base-level rise, the lower part of these incised valleys was respectively infilled with orbitolinid limestones and high-energy carbonate deposits influenced by tides. Further evidence of major relative sea-level drop and rise during the late early Aptian includes a detached backstepping carbonate platform of reduced extension, underlain and overlain by basinal marly deposits, which flourished basinwards of a highstand platform margin. Although incised valleys or smaller-scale incisions are local features, evidence for relative declines in sea level can be identified from other evidence. For example, by the development of palaeokarst or by the presence of sharp or slightly erosive stratigraphic surfaces covered by deposits of higher energy influenced by tides, as observed in the late Aptian examples investigated herein. Comparable Aptian sedimentary features of subaerial exposure and subsequent transgressive genetic types of deposits have been observed in other basins across different tectonic plates, indicating that eustasy likely played a role in controlling accommodation changes during this stage. The discovery of new evidence for major relative Aptian sea-level fluctuations in various outcrops within the Maestrat Basin calls for further investigation in other underexplored Aptian platform carbonate successions in this basin. These investigations would contribute to a more accurate understanding of oceanographic dynamics during the Aptian Stage along the western margin of the Alpine Tethys.

Neural network-based method for determining vessel position by seabed relief

A seabed relief-based vessel position fixing model on the basis of a four-layered feedforward neural network is proposed. Hidden neurons have hyperbolic tangent activation functions. The model is constructed for 1-D case that can be considered as vessel motion throw a narrow channel or alongside fairway axis. A sequence of spot soundings is given for the network input. The linear coordinate registered for the last sounding forms the network output. The training set is formed by means of the intentional pseudorandom alteration of input samples in accordance with suspected limits of sea level variations and the constant error of its measurements. The validation set is not used. The Adamax algorithm is implemented for the neural network training. The maximum of absolute value of the prediction error is used as a performance criterion of the net. Modeling has been conducted with the Python programming language. The Tensorflow library is used for the creation, training and testing of the neural network. The depth is modelled as a piecewise polynomial function of the coordinate. The results of neural network testing with the use of noised input samples let to state that the neural net can determine a ship position by means of soundings with acceptable accuracy. Different combinations of the sea level error and the number of hidden neurons have been considered. For each of such combinations the network accuracy indicators have been calculated. The best results are obtained for the network with 100 hidden neurons per each layer.

Interannual sea-level variation around mainland Japan forced by subtropical North Pacific wind and its possible impact on the Tsugaru warm current

Interannual sea-level variation around mainland Japan forced by subtropical North Pacific wind and its possible impact on the Tsugaru warm current

Effects of the Last Deglaciation climate warming on hydrate dissociation in the northern South China Sea

Sea level and bottom water temperature variations caused by the Last Deglaciation climate warming impacted the stability of marine hydrates. In order to examine their influence on hydrate dissociation in the northern South China Sea (SCS), we conducted simulations to track the evolution of hydrate saturation and hydrate occurrence zone since the Last Deglaciation in the Dongsha Area, Shenhu Area, Xisha Area and Qiongdongnan Area. The amount of methane generated and subsequently released into seawater and atmosphere was also evaluated within the four areas. The simulation revealed the following results: (1) Hydrate dissociation induced by variations in sea level and bottom water temperature was observed in the Dongsha Area, Xisha Area and Qiongdongnan Area, but not in the Shenhu Area. (2) The water depth at which hydrate dissociation occurred ranged between 480 and 720 m, encompassing a hydrate dissociation area of approximately 1.54 × 1010 m2. This accounted for 6.68% of the northern South China Sea Area. (3) Since the Last Deglaciation, an estimation of 3.08 × 108–1.48 × 1010 m3 hydrates have dissociated, resulting in the release of 5.05 × 1010–2.43 × 1012 m3 methane. The generated methane migrated through the overlying sediments by means of central migration mode. 9.9 × 109–4.76 × 1011 m3 methane entered into the seawater, which will result in the formation of a weak acid affecting the marine environment. Meanwhile, 2.02 × 108–9.72 × 109 m3 methane entered into the atmosphere, which leads to an increase in greenhouse gas concentrations.

CHANGING EXTREME SEA LEVELS ALONG THE COAST OF MALAYSIA

This study examined extreme sea level (ESL) variations along the Malaysian coast using hourly sea level data from 17 tide gauge stations. The maximum observed ESLs varied from 1.26 m at Bintulu to 2.92 m at Port Klang, with tides playing a significant role in ESLs, especially along the west coast of Peninsular Malaysia. The spatial variation of seasonal ESLs showed a higher maximum of non-tidal residuals (0.8-1.1 m) along the east coast of Peninsular Malaysia during the northeast monsoon. This can be mainly attributed to the influence of the monsoon wind. Moreover, significant increases in ESLs were observed at 14 stations, largely due to rises in mean sea level. The interannual variability of ESL could be associated with the El Niño-Southern Oscillation at most sites except the northeast coast of Peninsular Malaysia. Interestingly, the interannual variability of the non-tidal residuals could be linked to the monsoon at sites located on the west coast of Peninsular Malaysia and East Malaysia. These findings provide valuable insights to relevant authorities for coastal planning, especially regarding flood risk management and the formulation of effective mitigation strategies.

Variability of the Indonesian Throughflow and Australian monsoon across the mid Pleistocene transition (IODP 363, Site U1483)

The Mid-Pleistocene Transition (MPT) between ∼1200 and ∼800 ka was associated with a major shift in global climate and was marked by a change in glacial/interglacial periodicity from ∼41 to ∼100 kyr that resulted in higher-amplitude sea-level variations and intensified glacial cooling. The sensitivity of the Indonesian Throughflow (ITF), and the Asian-Australian Monsoon dynamics to changing MPT climate remains controversial, although its understanding is important to constrain future climate projections. In this study, we analyzed radiolarian assemblages in core top samples retrieved during the RV Sonne Expedition 257 and in downcore samples from International Ocean Discovery Program (IODP) Site U1483 to estimate the variability in regional sea surface temperatures (SSTs), and to explore ITF dynamics in relation to glacio-eustatic sea-level variations and tropical monsoon strength during the MPT. Our results suggest that tropical monsoon strength and glacio-eustatic sea-level change influenced SST variations at Site U1483. Comparisons with SST data from the mid latitudes off Northwest Australia and the South China Sea suggest that SST variations at Site U1483 and in the ITF outflow into the Timor Sea are highly dependent on prevailing climate changes in the source region of the ITF, rather than on southern hemisphere. atmospheric circulation. In addition, comparisons of radiolarian abundances with X-ray fluorescence-scanning elemental data indicate that until ∼980 ka radiolarian productivity was higher during strong interglacial summer monsoons, likely because of the riverine runoff generated by monsoonal precipitation. However, at ∼980 ka pronounced winter monsoon cooling was associated with a re-organization of radiolarian production patterns in the Timor Sea.