@article {liu_pre-aged_2023,
	title = {Pre-aged terrigenous organic carbon biases ocean ventilation-age reconstructions in the North Atlantic},
	journal = {Nature Communications},
	volume = {14},
	number = {1},
	year = {2023},
	note = {Number: 1 Publisher: Nature Publishing Group},
	month = {06/2023},
	abstract = {Changes in ocean ventilation have been pivotal in regulating carbon sequestration and release on centennial to millennial timescales. However, paleoceanographic reconstructions documenting changes in deep-ocean ventilation using 14C dating, may bear multidimensional explanations, obfuscating the roles of ocean ventilation played on climate evolution. Here, we show that previously inferred poorly ventilated conditions in the North Atlantic were linked to enhanced pre-aged organic carbon (OC) input during Heinrich Stadial 1 (HS1). The 14C age of sedimentary OC was approximately 13,345 {\textpm} 692 years older than the coeval foraminifera in the central North Atlantic during HS1, which is coupled to a ventilation age of 5,169 {\textpm} 660 years. Old OC was mainly of terrigenous origin and exported to the North Atlantic by ice-rafting. Remineralization of old terrigenous OC in the ocean may have contributed to, at least in part, the anomalously old ventilation ages reported for the high-latitude North Atlantic during HS1.},
	keywords = {Carbon cycle, Marine chemistry, Palaeoceanography},
	issn = {2041-1723},
	doi = {10.1038/s41467-023-39490-6},
	url = {https://www.nature.com/articles/s41467-023-39490-6},
	author = {Liu, Jingyu and Wang, Yipeng and Jaccard, Samuel L. and Wang, Nan and Gong, Xun and Fang, Nianqiao and Bao, Rui}
}
@article {2542,
	title = {No iron fertilization in the equatorial Pacific Ocean during the last ice age},
	journal = {Nature},
	volume = {529},
	year = {2016},
	month = {Mar-01-2018},
	pages = {519 - 522},
	abstract = {The equatorial Pacific Ocean is one of the major high-nutrient, low-chlorophyll regions in the global ocean. In such regions, the consumption of the available macro-nutrients such as nitrate and phosphate is thought to be limited in part by the low abundance of the critical micro-nutrient iron1. Greater atmospheric dust deposition2 could have fertilized the equatorial Pacific with iron during the last ice age{\textemdash}the Last Glacial Period (LGP){\textemdash}but the effect of increased ice-age dust fluxes on primary productivity in the equatorial Pacific remains uncertain3, 4, 5, 6. Here we present meridional transects of dust (derived from the 232Th proxy), phytoplankton productivity (using opal, 231Pa/230Th and excess Ba), and the degree of nitrate consumption (using foraminifera-bound δ15N) from six cores in the central equatorial Pacific for the Holocene (0{\textendash}10,000 years ago) and the LGP (17,000{\textendash}27,000 years ago). We find that, although dust deposition in the central equatorial Pacific was two to three times greater in the LGP than in the Holocene, productivity was the same or lower, and the degree of nitrate consumption was the same. These biogeochemical findings suggest that the relatively greater ice-age dust fluxes were not large enough to provide substantial iron fertilization to the central equatorial Pacific. This may have been because the absolute rate of dust deposition in the LGP (although greater than the Holocene rate) was very low. The lower productivity coupled with unchanged nitrate consumption suggests that the subsurface major nutrient concentrations were lower in the central equatorial Pacific during the LGP. As these nutrients are today dominantly sourced from the Subantarctic Zone of the Southern Ocean, we propose that the central equatorial Pacific data are consistent with more nutrient consumption in the Subantarctic Zone, possibly owing to iron fertilization as a result of higher absolute dust fluxes in this region7, 8. Thus, ice-age iron fertilization in the Subantarctic Zone would have ultimately worked to lower, not raise, equatorial Pacific productivity.},
	keywords = {Biogeochemistry, Palaeoceanography},
	issn = {0028-0836},
	doi = {10.1038/nature16453},
	url = {http://www.nature.com/doifinder/10.1038/nature16453},
	author = {Costa, K. M. and McManus, J. F. and Anderson, R. F. and Ren, H. and Sigman, D. M. and Winckler, G. and Fleisher, M. Q. and Marcantonio, F. and Ravelo, A. C.}
}
@article {2559,
	title = {Climatic and biotic thresholds of coral-reef~shutdown},
	journal = {Nature Climate Change},
	volume = {5},
	year = {2015},
	month = {Nov-02-2016},
	pages = {369 - 374},
	abstract = {Climate change is now the leading cause of coral-reef degradation and is altering the adaptive landscape of coral populations1, 2. Increasing sea temperatures and declining carbonate saturation states are inhibiting short-term rates of coral calcification, carbonate precipitation and submarine cementation3, 4, 5. A critical challenge to coral-reef conservation is understanding the mechanisms by which environmental perturbations scale up to influence long-term rates of reef-framework construction and ecosystem function6, 7. Here we reconstruct climatic and oceanographic variability using corals sampled from a 6,750-year core from Pacific Panam{\'a}. Simultaneous reconstructions of coral palaeophysiology and reef accretion allowed us to identify the climatic and biotic thresholds associated with a 2,500-year hiatus in vertical accretion beginning ~4,100 years ago8. Stronger upwelling, cooler sea temperatures and greater precipitation{\textemdash}indicators of La Ni{\~n}a-like conditions{\textemdash}were closely associated with abrupt reef shutdown. The physiological condition of the corals deteriorated at the onset of the hiatus, corroborating theoretical predictions that the tipping points of radical ecosystem transitions should be manifested sublethally in the biotic constituents9. Future climate change could cause similar threshold behaviours, leading to another shutdown in reef development in the tropical eastern Pacific.},
	keywords = {Climate-change ecology, Palaeoceanography, Palaeoclimate, Palaeoecology},
	issn = {1758-678X},
	doi = {10.1038/nclimate2541},
	url = {http://www.nature.com/doifinder/10.1038/nclimate2541},
	author = {Toth, Lauren T. and Aronson, Richard B. and Cobb, Kim M. and Cheng, Hai and Edwards, R. Lawrence and Grothe, Pamela R. and Sayani, Hussein R.}
}
@article {2586,
	title = {North Atlantic forcing of tropical Indian Ocean climate},
	journal = {Nature},
	volume = {509},
	year = {2014},
	month = {Jun-04-2016},
	pages = {76 - 80},
	abstract = {The response of the tropical climate in the Indian Ocean realm to abrupt climate change events in the North Atlantic Ocean is contentious. Repositioning of the intertropical convergence zone is thought to have been responsible for changes in tropical hydroclimate during North Atlantic cold spells1, 2, 3, 4, 5, but the dearth of high-resolution records outside the monsoon realm in the Indian Ocean precludes a full understanding of this remote relationship and its underlying mechanisms. Here we show that slowdowns of the Atlantic meridional overturning circulation during Heinrich stadials and the Younger Dryas stadial affected the tropical Indian Ocean hydroclimate through changes to the Hadley circulation including a southward shift in the rising branch (the intertropical convergence zone) and an overall weakening over the southern Indian Ocean. Our results are based on new, high-resolution sea surface temperature and seawater oxygen isotope records of well-dated sedimentary archives from the tropical eastern Indian Ocean for the past 45,000 years, combined with climate model simulations of Atlantic circulation slowdown under Marine Isotope Stages 2 and 3 boundary conditions. Similar conditions in the east and west of the basin rule out a zonal dipole structure as the dominant forcing of the tropical Indian Ocean hydroclimate of millennial-scale events. Results from our simulations and proxy data suggest dry conditions in the northern Indian Ocean realm and wet and warm conditions in the southern realm during North Atlantic cold spells.},
	keywords = {Palaeoceanography, Palaeoclimate},
	issn = {0028-0836},
	doi = {10.1038/nature13196},
	url = {http://www.nature.com/doifinder/10.1038/nature13196},
	author = {Mohtadi, Mahyar and Prange, Matthias and Oppo, Delia W. and De Pol-Holz, Ricardo and Merkel, Ute and Zhang, Xiao and Steinke, Stephan and {\"u}ckge, Andreas}
}
@article {2545,
	title = {Persistent export of 231Pa from the deep central Arctic Ocean over the past 35,000 years},
	journal = {Nature},
	volume = {497},
	year = {2013},
	month = {May-05-2015},
	pages = {603 - 606},
	abstract = {The Arctic Ocean has an important role in Earth{\textquoteright}s climate, both through surface processes1 such as sea-ice formation and transport, and through the production and export of waters at depth that contribute to the global thermohaline circulation2, 3. Deciphering the deep Arctic Ocean{\textquoteright}s palaeo-oceanographic history is a crucial part of understanding its role in climatic change. Here we show that sedimentary ratios of the radionuclides thorium-230 (230Th) and protactinium-231 (231Pa), which are produced in sea water and removed by particle scavenging on timescales of decades to centuries, respectively4, record consistent evidence for the export of 231Pa from the deep Arctic and may indicate continuous deep-water exchange between the Arctic and Atlantic oceans throughout the past 35,000 years. Seven well-dated box-core records provide a comprehensive overview of 231Pa and 230Th burial in Arctic sediments during glacial, deglacial and interglacial conditions. Sedimentary 231Pa/230Th ratios decrease nearly linearly with increasing water depth above the core sites, indicating efficient particle scavenging in the upper water column and greater influence of removal by lateral transport at depth. Although the measured 230Th burial is in balance with its production in Arctic sea water, integrated depth profiles for all time intervals reveal a deficit in 231Pa burial that can be balanced only by lateral export in the water column. Because no enhanced sink for 231Pa has yet been found in the Arctic, our records suggest that deep-water exchange through the Fram strait may export 231Pa. Such export may have continued for the past 35,000 years, suggesting a century-scale replacement time for deep waters in the Arctic Ocean since the most recent glaciation and a persistent contribution of Arctic waters to the global ocean circulation.},
	keywords = {Marine chemistry, Palaeoceanography, Palaeoclimate},
	issn = {0028-0836},
	doi = {10.1038/nature12145},
	url = {http://www.nature.com/doifinder/10.1038/nature12145},
	author = {Hoffmann, Sharon S. and McManus, Jerry F. and Curry, William B. and Brown-Leger, L. Susan}
}
@article {2546,
	title = {Transient stratification as the cause of the North Pacific productivity spike during deglaciation},
	journal = {Nature Geoscience},
	volume = {6},
	year = {2013},
	month = {Feb-07-2014},
	pages = {622 - 626},
	abstract = {During the B{\o}lling{\textendash}Aller{\o}d warm period of the last deglaciation, about 14 kyr ago, there was a strong and pervasive spike in primary productivity in the North Pacific Ocean1. It has been suggested that this productivity event was caused by an influx of the micronutrient iron from surrounding continental shelves as they were flooded by sea-level rise2. Here we test this hypothesis by comparing numerous proxies of productivity with iron flux and provenance measured from a core from the subarctic Pacific Ocean. We find no evidence for an abrupt deglacial pulse of iron from any source at the time of peak productivity. Instead, we argue that the deglacial productivity peak was caused by two stepwise events. First, deep convection during early deglaciation increased nutrient supply to the surface but also increased the depth of the mixed layer, which pushed surface production deeper in the water column and induced light limitation. A subsequent input of meltwater from northern American ice sheets then stratified the water column, which relieved light limitation while leaving the surface waters enriched in nutrients. We conclude that iron plays, at most, a secondary role in controlling productivity during the glacial and deglacial periods in the subarctic Pacific Ocean.},
	keywords = {Biogeochemistry, Marine biology, Marine chemistry, Palaeoceanography},
	issn = {1752-0894},
	doi = {10.1038/ngeo1873},
	url = {http://www.nature.com/doifinder/10.1038/ngeo1873},
	author = {Lam, Phoebe J. and Robinson, Laura F. and Blusztajn, Jerzy and Li, Camille and Cook, Mea S. and McManus, Jerry F. and Keigwin, Lloyd D.}
}
@conference {1278,
	title = {The Effect of Different Acid Treatments on the Radiocarbon Age of Sedimentary Organic Matter},
	booktitle = {EOS, Transactions, American Geophysical Union},
	year = {2001},
	note = {Date revised - 2007-02-01SuppNotes - Session: OS41A 9 The Truth About Paleoceanographic Proxies - What Are They Really Telling Us III Posters.Last updated - 2016-05-27},
	month = {January 2001},
	publisher = {American Geophysical Union, 2000 Florida Ave., N.W. Washington DC 20009 USA, [mailto:service@agu.org]},
	organization = {American Geophysical Union, 2000 Florida Ave., N.W. Washington DC 20009 USA, [mailto:service@agu.org]},
	abstract = {To date the bulk organic carbon in marine sediments it is necessary to first remove any inorganic carbon present by acidification. We tested three different acid treatments to see how the different methods affected the stable and radio-carbon isotopic values of the remaining organic matter. The standard NOSAMS method is to react the sediment with repeated aliquots of1.2N HCl until no visible dissolution reaction is present. The remaining sediment is then rinsed with distilled water. This method leaves a carbonate-free sediment that is easy to combust but suffers from the possible removal of acid-soluble organic matter. We compared this method to two methods that do not require rinsing of the sediments after acid treatment--a vapor phase acidification method using concentrated HCl (Hedges and Stern, 1984) and an in situ acidification with sulfurous acid (Verardo et al., 1990). Scaling these methods up to deal with the amount of sediment required for a radiocarbon date can present challenges that are not evident when dealing with the small quantities required for a percent organic carbon measurement. Vapor phase acidification of high carbonate sediments leaves hygroscopic salts that can impede sample combustion. Sulfurous acid is a weak acid and it is very difficult to determine when all the carbonate has been removed from a sediment sample. We tested sediments from 6 locations in (or near) the Atlantic Ocean that represented riverine, estuarine, and marine environments as well as a range of both organic and inorganic concentrations. We will present the isotopic results for these sediments and evaluate what is the most appropriate method to use. Hedges J.I. and J.H. Stern (1984) Limnol. Oceanogr. 29, 657-663. Verardo D.J., P.N. Froelich and A. McIntyre (1990) Deep-Sea Res. 37, 157-165.},
	keywords = {A, Atlantic, Acidification, Brackish, Brackishwater environment, carbon cycling, Chronostratigraphy, Estuarine sedimentation, organic carbon, organic matter, Palaeoceanography, Radioactivity and radioisotopes, Radiocarbon dating, Sediment chemistry, Stable isotopes},
	url = {https://search.proquest.com/docview/19468089?accountid=29119},
	author = {Batista, F and McNichol, A P and Gerlach, D S}
}
