the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 05 Dec 2024
Decreasing foraminiferal flux in response to ongoing climate change in the Santa Barbara Basin, California
Abstract. The rapid response of foraminiferal assemblages to changing climate makes their shells an invaluable geological record of the past. However, the time frame over which foraminifera respond to climatic signals and the specific drivers influencing assemblage composition and abundance remain obscure. We focus on the impact of ongoing, anthropogenic climate change on planktic foraminifera in the California Current ecosystem, which would appear as a nearly instantaneous event in the sediment record. The Santa Barbara Basin sediment trap, located off the coast of California, USA since 1993, provides a 28-year record of particulate and foraminiferal flux to the basin’s seafloor. The sediment trap captures the superposition of the annual cycle of seasonal upwelling, Pacific multiannual El Niño-Southern Oscillation-driven temperature changes, and anthropogenically forced climate change. We present data on planktic foraminiferal flux collected between 2014–2021, at two-week intervals (164 samples, 60,006 individuals) and compare results to previously published data from 1993–1998. Consistent with previous studies, the most abundant species from 2014–2021 were Globigerina bulloides, Neogloboquadrina incompta, and Turborotalita quinqueloba, with peak fluxes occurring in the spring and summer. Lower fluxes and an increase in the abundance of N. incompta and subtropical species characterize the winter season. We find a 37.9 % decrease in total foraminiferal flux relative to the 1990s, primarily driven by a decrease in G. bulloides abundance. This decrease is accompanied by a 21.9 % overall reduction in calcium carbonate flux. We also find a decrease in the relative abundance of subtropical species (Globigerinoides ruber, Orbulina universa, Neogloboquadrina dutertrei) and their fluxes compared to the 1990s, contrary to expectations if assemblages and fluxes were to follow anthropogenic warming signals. We hypothesize that the observed decrease in subtropical species abundance and flux is likely related to an increase in acidification and in the timing and magnitude of upwelling along the California coast. The extremely rapid responses of foraminifera to ongoing changes in carbonate chemistry and temperature suggest that climate change is already having a meaningful impact on coastal carbon cycling. The observed decrease in particulate inorganic carbon (PIC) flux relative to particulate organic carbon (POC) flux may facilitate increased oceanic uptake of atmospheric CO2.
- Preprint
(2609 KB) - Metadata XML
- BibTeX
- EndNote
Status: final response (author comments only)
-
RC1: 'Comment on egusphere-2024-3374', Anonymous Referee #1, 11 Jan 2025
Harvard et al. showed assemblages and fluxes of planktic foraminifers in sediment trap samples moored at Santa Barbara Basin in 2014-2021. Compared to data from 1993-1998, fluxes especially G. bulloides decreases. Contrary to the anthropogenic warming trend, relative abundances of subtroical species also decreases. Authors hypothesize widely acidified seawater in the upwelling is related to the foraminiferal changes. Hard work of authors provides a useful dataset to capture the rapid shift of foraminiferal assemblages and abundances in thirty years. Although the analyses are conventional methodology, the novelty of dataset showing the potential impact of environmental change is suitable for the scope of the journal.
I have following major comments.
First, assemblage analyses of foraminifer do not yield direct relationships between environmental parameters and fluxes or assemblages. As authors shown in Figs. 5 and 6 and table 2, related environmental factors to fluxes of the most abundant G. bulloides is unclear. In line 438-441, G.bulloides is an indicator of primary productivity but is negatively correlated to OC and opal, which are primary productivity indicators. And I consider that negative association between G. bulloides fluxes and pH means acidification may not negatively affect G. bulloides fluxes (I think this may be a descriptive problem).They appears to be a contradiction. Direct impact of acidification on foraminiferal fluxes is not confirmed by the results demonstrated in the manuscript. The statistical analysis does not confirm that acidification is related to the change of foraminiferal assemblages.
Authors do not compare fluctuation of environmental parameters and foraminiferal fluxes between 2014-2021 and 1993-1998. I understand this is difficult, but the drivers in the decline of foraminifer fluxes could not determined directly only by relationship environmental parameters and fluxes in 2014-2021. For example, because major species do not have symbionts and depend on feeding, is flux decreases related to the possibility of change of food in the basin? Therefore, I recommend that the authors make some revisions to clarify their study.
The followings is minor comments;
In manuscript, data of sinking particle components are missing. It is difficult to confirm the discussion and statistical analyses without the data.
Citation: https://doi.org/10.5194/egusphere-2024-3374-RC1 -
RC2: 'Comment on egusphere-2024-3374', Anonymous Referee #2, 22 Jan 2025
The study of Harvard et al. uses a 28-year sediment trap record to investigate the impact of ongoing climate change on planktonic foraminiferal flux in the Santa Barbara Basin. The authors compare recent data to older records and find a significant decline in foraminiferal flux, particularly for Globigerina bulloides, alongside reduced calcium carbonate flux. They hypothesize that acidification and changes in upwelling dynamics are key drivers of these trends, highlighting the rapid response of foraminifera to environmental changes.
Firstly, I would like to thank the authors for providing this valuable long-term time series of planktonic foraminifera flux in the Santa Barbara Basin. This dataset represents an important environmental and ecological record, offering critical insights into the impacts of climate change on marine ecosystems.
If true, the decline in foraminifera shown here is alerting. However, one concern lies in the comparison between the 2014–2021 sediment trap data and the older dataset from 1993–1998. The study does not account for potential long-term changes in the size of planktonic foraminifera, which are thought to decrease due to warming/climate change (Deutsch et al., 2022) and especially during intensified upwelling (10.22541/au.171987328.88940417/v1). As the measurements are constrained to specimens larger than 125 microns, it is possible that smaller specimens, potentially more abundant over time, are passing through the sieve. This could artificially amplify the reported decline in abundance and flux. (Perhaps the fact that T. quinqueloba is a small species explains its flux consistency.) Addressing/discussing this aspect would strengthen the conclusions and provide a more accurate assessment of climate-driven changes in foraminiferal populations.
The authors emphasize ocean acidification as a major factor influencing planktonic foraminifera fluxes and abundances but focus only on its biotic effects. While basin waters are clearly acidifying due to anthropogenic emissions and intensified upwelling, the impact especially on living foraminifera remains debated (Leung et al., 2022). What is certain, however, is that acidification promotes post-mortem shell dissolution (unprotected shells), with significant carbonate loss occurring in the upper 300m (Kwon et al., 2024). Oxygen-rich waters can also intensify dissolution/acidification due to enhanced organic matter oxidation. A key concern is thus whether the observed decline in foraminiferal abundances in sediment trap data may instead reflect post-mortem dissolution of their shells in increasingly acidified waters. Smaller specimens, which are more prone to dissolution, may be disproportionately affected, especially given the potential long-term size reduction in planktonic foraminifera due to climate change. This raises the possibility that the decline in abundance is not solely a biological signal but also a taphonomic one. Greater clarity on how acidification influences both living populations and the preservation of their fossil remains would provide a more robust interpretation of these data.
Further on taphonomy, some specimens in Figure A1 appear slightly etched. Could those be resuspended material in the traps? Were any benthic specimens observed? This is a usual phenomenon is some sediment traps.
Minor
Methods: Please consider briefly explaining in the methods section what loadings and directions represent in Canonical Correlation Analysis to aid reader understanding.Lines 65-69: Partly true. Thinning can also be due to adaptation. Results indicate that salinity significantly influences pteropod distribution (Johnson et al., 2023), while their biomineralization is affected by salinity due to its role in buoyancy regulation (Manno et al., 2012). Similarly, calcification changes for buoyancy regulation have also been suggested for foraminifera (Zarkogiannis et al., 2019).
In a future submission please consider changing planktic to planktonic. The correct adjective form of plankton is planktonic. The adjectives of Greek nouns ending in -on get the suffix -ic in the end like plankton – planktonic, bion – bionic, lacon – laconic. This is different to nouns ending in -os, which lose the ending -os to the previous consonant by replacing it with -ic, like bentos – benthic, cosmos – cosmic or chronos – chronic.
References
Deutsch, C., Penn, J. L., Verberk, W. C. E. P., Inomura, K., Endress, M.-G., and Payne, J. L.: Impact of warming on aquatic body sizes explained by metabolic scaling from microbes to macrofauna, Proc. Nat. Acad. Sci., 119, e2201345119, 10.1073/pnas.2201345119, 2022.
Johnson, R., Manno, C., and Ziveri, P.: Shelled pteropod abundance and distribution across the Mediterranean Sea during spring, Prog. Oceanogr., 210, 102930, 10.1016/j.pocean.2022.102930, 2023.
Kwon, E. Y., Dunne, J. P., and Lee, K.: Biological export production controls upper ocean calcium carbonate dissolution and CO2 buffer capacity, Science Advances, 10, eadl0779, 10.1126/sciadv.adl0779, 2024.
Leung, J. Y. S., Zhang, S., and Connell, S. D.: Is Ocean Acidification Really a Threat to Marine Calcifiers? A Systematic Review and Meta-Analysis of 980+ Studies Spanning Two Decades, Small, 18, 2107407, 10.1002/smll.202107407, 2022.
Manno, C., Morata, N., and Primicerio, R.: Limacina retroversa's response to combined effects of ocean acidification and sea water freshening, Estuar. Coast. Shelf Sci., 113, 163-171, 10.1016/j.ecss.2012.07.019, 2012.
Zarkogiannis, S. D., Antonarakou, A., Tripati, A., Kontakiotis, G., Mortyn, P. G., Drinia, H., and Greaves, M.: Influence of surface ocean density on planktonic foraminifera calcification, Sci. Rep., 9, 533, 10.1038/s41598-018-36935-7, 2019.Citation: https://doi.org/10.5194/egusphere-2024-3374-RC2
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 121 | 26 | 5 | 152 | 1 | 3 |
- HTML: 121
- PDF: 26
- XML: 5
- Total: 152
- BibTeX: 1
- EndNote: 3
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1