Periodic Reporting for period 1 - T-SECTOR (Testing solid earth climate connections through mid ocean ridge time series)
Reporting period: 2023-10-01 to 2025-03-31
A key challenge in understanding the Earth system is quantifying the feedback between climate and the solid Earth, which requires long-term time series. One critical time series is the sea level record, which fluctuated between ice ages and warm periods over millions of years. Volcanic activity at mid-ocean ridges (MORs), where 80% of the Earth’s volcanism occurs, is sensitive to changes in the pressure on the ridges, but its response to glacial cycles, causing sea level fluctuations, is largely unknown.
The key hypothesis that we plan to test is if volcanism at mid-ocean ridges has oscillated inversely with climate induced sea level change. During glacial periods, lower sea level (due to storage of seawater in glaciers on land) resulted in less hydrostatic pressure on the ridges, thus there was enhanced pressure-release induced melting of the upper mantle, creating thicker oceanic crust and greater amounts of volcanism and hydrothermal activity at the earth’s surface. During interglacials, sea level is higher, suppressing mantle melting, resulting in thinner newly formed oceanic crust and less volcanic and hydrothermal activity along the ridges.
Models confirm that sea level fluctuations can affect crustal thickness, lava chemistry, and hydrothermal activity at MORs. However, creating high-resolution time series of these variations has been difficult because sediments quickly cover the sea floor as it moves away from the ridge, making direct sampling a challenge. Recent studies and eruptions on mid-ocean ridges (e.g. the eruption on April 29, 2025 at 9.83°N and 104.3°W on the summit of the East Pacific Rise at 2500 m depth) show that glass fragments are formed during MOR eruptions, distributed for kilometres from the eruptive sites, and preserved in nearby carbonate-rich sediments, which can be sampled by gravity coring. These sediments can be precisely dated using oxygen isotope stratigraphy, providing a record of ridge eruptions (from the composition of volcanic glass hosted by the sediments) and hydrothermal activity (trace metals deposited on sediment grains).
Through closely spaced cores collected along transects perpendicular to the ridge axis during multiple research cruises, we aim to create a high-resolution time series of volcanic and hydrothermal activity directly linked to climate records. Using seismic techniques, we will track changes in crustal thickness over time. Our aim is to gather integrated data from slow, intermediate, and fast-spreading ridge segments over the past 1.5 million years in unprecedented detail. These results will allow us to test the influence of glacial cycles on MOR processes and provide the first high-resolution time series of ocean-ridge magmatism, opening a new frontier in scientific exploration.
The key hypothesis that we plan to test is if volcanism at mid-ocean ridges has oscillated inversely with climate induced sea level change. During glacial periods, lower sea level (due to storage of seawater in glaciers on land) resulted in less hydrostatic pressure on the ridges, thus there was enhanced pressure-release induced melting of the upper mantle, creating thicker oceanic crust and greater amounts of volcanism and hydrothermal activity at the earth’s surface. During interglacials, sea level is higher, suppressing mantle melting, resulting in thinner newly formed oceanic crust and less volcanic and hydrothermal activity along the ridges.
Models confirm that sea level fluctuations can affect crustal thickness, lava chemistry, and hydrothermal activity at MORs. However, creating high-resolution time series of these variations has been difficult because sediments quickly cover the sea floor as it moves away from the ridge, making direct sampling a challenge. Recent studies and eruptions on mid-ocean ridges (e.g. the eruption on April 29, 2025 at 9.83°N and 104.3°W on the summit of the East Pacific Rise at 2500 m depth) show that glass fragments are formed during MOR eruptions, distributed for kilometres from the eruptive sites, and preserved in nearby carbonate-rich sediments, which can be sampled by gravity coring. These sediments can be precisely dated using oxygen isotope stratigraphy, providing a record of ridge eruptions (from the composition of volcanic glass hosted by the sediments) and hydrothermal activity (trace metals deposited on sediment grains).
Through closely spaced cores collected along transects perpendicular to the ridge axis during multiple research cruises, we aim to create a high-resolution time series of volcanic and hydrothermal activity directly linked to climate records. Using seismic techniques, we will track changes in crustal thickness over time. Our aim is to gather integrated data from slow, intermediate, and fast-spreading ridge segments over the past 1.5 million years in unprecedented detail. These results will allow us to test the influence of glacial cycles on MOR processes and provide the first high-resolution time series of ocean-ridge magmatism, opening a new frontier in scientific exploration.
Within the first 1.5 years, the T-SECTOR team acquired, installed and tested new instruments to carry out the project, as well as developing new sample preparation and chemical separation techniques. The most important tasks carried out are described in the following:
• New Ocean Bottom Seismometers (OBS) developed and built at GEOMAR to determine crustal thickness on R/V Sonne cruise SO314 to the Southern East Pacific Rise (SEPR)
• New mass spectrometer MAT253 Plus IRMS purchased and set up at GEOMAR for analyses of C and O isotopes on benthic foraminifera to establish high-resolution chronologies (age models) of sediment cores in order to construct time series of hydrothermal and volcanic activity. Measurements carried out on cores from Reykjanes cruise (MSM119).
• New AGILENT 8900 TQ-ICP-MS with RESOlution-SE 193nm excimer laser purchased and set up at Harvard University for the determination of major and trace element concentrations in sediment-hosted volcanic glasses. Hundreds of glass shards from Reykjanes sediment gravity cores (obtained on R/V Maria S Merian cruise MSM119) have been analysed with the new instrument.
• Low-blank clean room laboratories for determination of radiogenic Sr, Nd, Hf and Pb isotope compositions have been completed. New ion exchange techniques are being developed to reduce the blanks for these analyses. New iCCAP-TQ ICP-MS and NEOMA MC-ICP-MS have been acquired, installed and set up in order to determine elemental concentrations at ≤ppb level and for high-sensitivity, high-precision and accuracy isotope ratio measurements of MORB glass shards. Routines for analysing minimal amounts of the aforementioned isotope systems are presently being developed.
In addition to the acquisition, testing and development of new instruments and techniques, it was necessary to write, submit and revise the research expedition proposals to enable the T-SECTOR research team to retrieve the samples and data needed to carry out the project objectives. Three sets of research expeditions dedicated to the T-SECTOR project have been approved and all but one scheduled: 1) Intermediate-spreading ridge: A US proposal for two Cleft Segment, Juan de Fuca Ridge (NE Pacific Ocean) cruises, one to carry out autonomous unterwater vehicle (AUV) seafloor mapping and one for gravity and rock (wax) coring. The first of these research expeditions was scheduled on the research vessel Sally Ridge for April 30 through May 11 2025. 2) Fast-spreading ridge: A German research expedition to the South East Pacific Rise with the R/V Sonne (SO314) is scheduled for August to October 2025. 3) Two German research expeditions (SO321 leg 1 to carry out seabed drilling and leg 2 to carry out gravity and rock coring) to the Cleft Segment are scheduled for August/September 2026.
The T-SECTOR team participated in a research cruise to the slow-spreading Reykjanes Ridge (North Atlantic Ocean) with the Maria S. Merian in 2024 (MSM119). Gravity cores were taken near the spreading centre. Basaltic glass samples were taken from the cores and analysed for major and trace elements at Harvard University. Isotope analyses of the authigenic sedimentary phases and basaltic glasses are currently being prepared at GEOMAR.
• New Ocean Bottom Seismometers (OBS) developed and built at GEOMAR to determine crustal thickness on R/V Sonne cruise SO314 to the Southern East Pacific Rise (SEPR)
• New mass spectrometer MAT253 Plus IRMS purchased and set up at GEOMAR for analyses of C and O isotopes on benthic foraminifera to establish high-resolution chronologies (age models) of sediment cores in order to construct time series of hydrothermal and volcanic activity. Measurements carried out on cores from Reykjanes cruise (MSM119).
• New AGILENT 8900 TQ-ICP-MS with RESOlution-SE 193nm excimer laser purchased and set up at Harvard University for the determination of major and trace element concentrations in sediment-hosted volcanic glasses. Hundreds of glass shards from Reykjanes sediment gravity cores (obtained on R/V Maria S Merian cruise MSM119) have been analysed with the new instrument.
• Low-blank clean room laboratories for determination of radiogenic Sr, Nd, Hf and Pb isotope compositions have been completed. New ion exchange techniques are being developed to reduce the blanks for these analyses. New iCCAP-TQ ICP-MS and NEOMA MC-ICP-MS have been acquired, installed and set up in order to determine elemental concentrations at ≤ppb level and for high-sensitivity, high-precision and accuracy isotope ratio measurements of MORB glass shards. Routines for analysing minimal amounts of the aforementioned isotope systems are presently being developed.
In addition to the acquisition, testing and development of new instruments and techniques, it was necessary to write, submit and revise the research expedition proposals to enable the T-SECTOR research team to retrieve the samples and data needed to carry out the project objectives. Three sets of research expeditions dedicated to the T-SECTOR project have been approved and all but one scheduled: 1) Intermediate-spreading ridge: A US proposal for two Cleft Segment, Juan de Fuca Ridge (NE Pacific Ocean) cruises, one to carry out autonomous unterwater vehicle (AUV) seafloor mapping and one for gravity and rock (wax) coring. The first of these research expeditions was scheduled on the research vessel Sally Ridge for April 30 through May 11 2025. 2) Fast-spreading ridge: A German research expedition to the South East Pacific Rise with the R/V Sonne (SO314) is scheduled for August to October 2025. 3) Two German research expeditions (SO321 leg 1 to carry out seabed drilling and leg 2 to carry out gravity and rock coring) to the Cleft Segment are scheduled for August/September 2026.
The T-SECTOR team participated in a research cruise to the slow-spreading Reykjanes Ridge (North Atlantic Ocean) with the Maria S. Merian in 2024 (MSM119). Gravity cores were taken near the spreading centre. Basaltic glass samples were taken from the cores and analysed for major and trace elements at Harvard University. Isotope analyses of the authigenic sedimentary phases and basaltic glasses are currently being prepared at GEOMAR.
T-SECTOR aims to open a new time dimension to ocean ridge studies, and to provide definite tests of the hypothesis, backed by theory, that sea level change (climate) influences ridge volcanism (solid Earth processes). Using data on the composition of mid-ocean-ridge-basalts obtained from sediment-hosted glasses, we aim to obtain time-series at an unprecedented resolution of 5-10ka over ≥1.5Ma uniquely combined with records of hydrothermal activity in the same sediments and with data on crustal thickness and seafloor morphology. The project also proposes a novel approach to construct time series of mid-ocean-ridge-basalt composition through seabed drilling, which will enable investigation of crustal production and other magmatic (volcanic and plutonic) processes at an unprecedented level. Once established, these approaches can also be used to construct time series of other seafloor volcanic systems. These time series have the potential to transform our understanding of seafloor spreading processes and the scale of heterogeneities in the underlying mantle. They will help us understand the feedback between glacial/interglacial climate and earth processes, providing new insights into enhanced magmatism during glacial cycles and the linked emission of CO2 into the atmosphere.