Periodic Reporting for period 1 - REEFCLAM (GSnapshots of tropical Pacific climate variability during the time of Lapita ocean voyaging: giant clam fossils from Fijian shell middens as high resolution archives of climate information.)
Berichtszeitraum: 2021-07-01 bis 2023-06-30
Understanding how Earth’s climate behaved before industrialisation is essential for predicting future climate change. Instrumental records extend back only ~150 years (a period already influenced by human activity) making them too short to the capture ‘background’ states of natural variability needed to test and improve climate models. These are the same models used to inform climate policy decisions and for guiding adaptation strategies in vulnerable Pacific Island communities. To look further back in time, scientists rely on past climate (paleoclimate) records based on ‘climate proxies’ such as chemical signals preserved in sediments, corals, and shells.
The tropical southwest Pacific is especially important, as it hosts two major climate systems: the El Niño–Southern Oscillation (ENSO) and the South Pacific Convergence Zone (SPCZ). These influence weather patterns far beyond the Pacific, yet the region remains underrepresented in high resolution paleoclimate datasets, particularly for the late Holocene (roughly the last 4,000 years). This gap hinders model development and limits understanding of how climate variability may have shaped past societies.
The REEFCLAM project aimed to address this by reconstructing seasonally resolved climate records from giant clam (Tridacnidae) shells in Fijian archaeological sites, dated to ~3,000 years before present (BP). Giant clams grow daily and annual layers that record sea surface temperature and salinity via geochemical climate proxies, such as stable oxygen isotopes. Further, giant clams were consumed and left behind in large quantities by the Lapita people, the pioneering voyagers who settled Remote Oceania ~2,500–3,200 years ago. This project used a unique collection of Lapita-aged shells from Fiji, donated/collected by the PI and staff at the Fiji Museum. By analysing physical and chemical patterns in these shells, REEFCLAM sought to address vital gaps in late Holocene paleoclimate records from the tropical SW Pacific as well as investigate the climate conditions that coincided with one of the greatest feats of human migration in history.
The project had four main objectives:
1. Analyse modern giant clams from Fiji to determine how their shell chemistry and growth record environmental and climatic change.
2. Apply the same methods to Lapita-aged fossil clams to generate multi-year, seasonally resolved paleoclimate records.
3. Reconstruct sea surface temperature and salinity variability, with a focus on ENSO and SPCZ dynamics.
4. Place these results in context by comparing them with records from other parts of the Holocene and elsewhere in the Pacific and examine the mean climate state during the Lapita settlement period.
The project was carried out in close collaboration with the Fiji Museum.
Key conclusions
All major objectives were achieved. A successful field campaign, carried out in close collaboration with the Fiji Museum, secured both modern and fossil clam specimens. Twelve fossil shells were confirmed as Lapita-aged (~2,700-3,100 BP), providing an invaluable archive of climate information. One was dated as ~5800 BP, providing an important mid-Holocene comparison. Laboratory analyses of growth patterns, isotopes, and trace elements are already producing high-resolution insights into past ocean conditions and are helping to refine how giant clams can be used as climate recorders. Some laboratory measurements are still being processed, with final interpretation expected by 2026. However, the project has already generated new results on mid-to-late Holocene Pacific climate variability, improved understanding of how giant clams archive environmental signals, and established robust methods for identifying well-preserved fossil material.
In short, REEFCLAM has filled an important gap in tropical Pacific paleoclimate data, strengthened collaborations with Pacific institutions, and provided new perspectives on both climate dynamics and human history in Oceania.
The tropical southwest Pacific is especially important, as it hosts two major climate systems: the El Niño–Southern Oscillation (ENSO) and the South Pacific Convergence Zone (SPCZ). These influence weather patterns far beyond the Pacific, yet the region remains underrepresented in high resolution paleoclimate datasets, particularly for the late Holocene (roughly the last 4,000 years). This gap hinders model development and limits understanding of how climate variability may have shaped past societies.
The REEFCLAM project aimed to address this by reconstructing seasonally resolved climate records from giant clam (Tridacnidae) shells in Fijian archaeological sites, dated to ~3,000 years before present (BP). Giant clams grow daily and annual layers that record sea surface temperature and salinity via geochemical climate proxies, such as stable oxygen isotopes. Further, giant clams were consumed and left behind in large quantities by the Lapita people, the pioneering voyagers who settled Remote Oceania ~2,500–3,200 years ago. This project used a unique collection of Lapita-aged shells from Fiji, donated/collected by the PI and staff at the Fiji Museum. By analysing physical and chemical patterns in these shells, REEFCLAM sought to address vital gaps in late Holocene paleoclimate records from the tropical SW Pacific as well as investigate the climate conditions that coincided with one of the greatest feats of human migration in history.
The project had four main objectives:
1. Analyse modern giant clams from Fiji to determine how their shell chemistry and growth record environmental and climatic change.
2. Apply the same methods to Lapita-aged fossil clams to generate multi-year, seasonally resolved paleoclimate records.
3. Reconstruct sea surface temperature and salinity variability, with a focus on ENSO and SPCZ dynamics.
4. Place these results in context by comparing them with records from other parts of the Holocene and elsewhere in the Pacific and examine the mean climate state during the Lapita settlement period.
The project was carried out in close collaboration with the Fiji Museum.
Key conclusions
All major objectives were achieved. A successful field campaign, carried out in close collaboration with the Fiji Museum, secured both modern and fossil clam specimens. Twelve fossil shells were confirmed as Lapita-aged (~2,700-3,100 BP), providing an invaluable archive of climate information. One was dated as ~5800 BP, providing an important mid-Holocene comparison. Laboratory analyses of growth patterns, isotopes, and trace elements are already producing high-resolution insights into past ocean conditions and are helping to refine how giant clams can be used as climate recorders. Some laboratory measurements are still being processed, with final interpretation expected by 2026. However, the project has already generated new results on mid-to-late Holocene Pacific climate variability, improved understanding of how giant clams archive environmental signals, and established robust methods for identifying well-preserved fossil material.
In short, REEFCLAM has filled an important gap in tropical Pacific paleoclimate data, strengthened collaborations with Pacific institutions, and provided new perspectives on both climate dynamics and human history in Oceania.
Modern and fossil clam samples were collected in Fiji and prepared for analysis at Cardiff University. Fossil ages were confirmed by AMS radiocarbon dating, with 12 specimens identified as Lapita-aged (~2,700-3,100 BP) and one as mid-Holocene (~5,800 BP). Shells were analysed for preservation, daily growth rate, stable isotopes, and trace element/Ca ratios. These analyses yielded novel, publishable results on giant clam sclerochronology, diagenetic processes in aragonite, and mid-late Holocene Pacific climate variability.
Strategic objectives were addressed through Work Packages (WP) 1 to 2; scientific objectives were achieved through WP 3 to 5; career objectives were addressed through WP 6 to 7. A brief description of the accomplishments in each WP are outlined below:
• Fieldwork and strategy (WP1–2): Successful expeditions secured specimens, permits, and collaborations with Fijian partners.
• Modern clam analysis (WP3): Growth, stable isotope, and trace element(TE)/Ca profiles were produced from several specimens, establishing baseline datasets for comparison with fossil records.
• Fossil clam analysis (WP4): Growth, stable isotope, and trace element(TE)/Ca were generated from well-preserved fossil shells after diagenetic screening.
• Climate interpretation (WP5): Initial reconstructions provide new insights into seasonal and inter-annual variability during the Lapita period; final interpretations will follow once all isotope datasets are processed.
• Training and management (WP6): The Fellow gained advanced training in geochemical and statistical techniques, teaching and supervisory experience, and secured a permanent lectureship at Cardiff University.
• Dissemination (WP7): Results were presented at international/national conferences, outreach events, and through collaborations. Several publications were generated with several more in preparation.
Strategic objectives were addressed through Work Packages (WP) 1 to 2; scientific objectives were achieved through WP 3 to 5; career objectives were addressed through WP 6 to 7. A brief description of the accomplishments in each WP are outlined below:
• Fieldwork and strategy (WP1–2): Successful expeditions secured specimens, permits, and collaborations with Fijian partners.
• Modern clam analysis (WP3): Growth, stable isotope, and trace element(TE)/Ca profiles were produced from several specimens, establishing baseline datasets for comparison with fossil records.
• Fossil clam analysis (WP4): Growth, stable isotope, and trace element(TE)/Ca were generated from well-preserved fossil shells after diagenetic screening.
• Climate interpretation (WP5): Initial reconstructions provide new insights into seasonal and inter-annual variability during the Lapita period; final interpretations will follow once all isotope datasets are processed.
• Training and management (WP6): The Fellow gained advanced training in geochemical and statistical techniques, teaching and supervisory experience, and secured a permanent lectureship at Cardiff University.
• Dissemination (WP7): Results were presented at international/national conferences, outreach events, and through collaborations. Several publications were generated with several more in preparation.
The impacts of REEFCLAM have been far-reaching:
Scientific advances: The project has generated transformative insights across multiple fields, including a) giant clam geochemistry and physiology, b) mid-late Holocene Pacific climate dynamics and c) diagenetic screening in aragonite, with methodological developments in each field. The results will resonate well beyond geochemistry and paleoclimatology, engaging archaeologists, climate modelers, and historians of human settlement alike.
Societal relevance: The work provides new insights into past seasonal and interannual climate variability in the tropical SW Pacific, helping to improve climate models and refine predictions that guide policy and adaptation strategies. The findings also offer a rare glimpse into the climatic context for one of the greatest feats of human exploration, resonating with Pacific Island communities by connecting climate history with their cultural heritage.
Career and capacity building: The REEFCLAM fellowship not only advanced science but has also been pivotal in consolidating my career. It enabled the development of new collaborations, training in diverse skills, and the transition to an independent researcher. This personal and professional growth directly supported my success in securing a permanent lectureship and building the foundation to establish a research group at Cardiff University.
Scientific advances: The project has generated transformative insights across multiple fields, including a) giant clam geochemistry and physiology, b) mid-late Holocene Pacific climate dynamics and c) diagenetic screening in aragonite, with methodological developments in each field. The results will resonate well beyond geochemistry and paleoclimatology, engaging archaeologists, climate modelers, and historians of human settlement alike.
Societal relevance: The work provides new insights into past seasonal and interannual climate variability in the tropical SW Pacific, helping to improve climate models and refine predictions that guide policy and adaptation strategies. The findings also offer a rare glimpse into the climatic context for one of the greatest feats of human exploration, resonating with Pacific Island communities by connecting climate history with their cultural heritage.
Career and capacity building: The REEFCLAM fellowship not only advanced science but has also been pivotal in consolidating my career. It enabled the development of new collaborations, training in diverse skills, and the transition to an independent researcher. This personal and professional growth directly supported my success in securing a permanent lectureship and building the foundation to establish a research group at Cardiff University.