Retracted: Plio‐Pleistocene Indonesian Throughflow Variability Drove Eastern Indian Ocean Sea Surface Temperatures

Abstract

Ocean gateways facilitate circulation between ocean basins, thereby impacting global climate. The Indonesian Gateway transports water from the Pacific to the Indian Ocean via the Indonesian Throughflow (ITF) and drives the strength and intensity of the modern Leeuwin Current, which carries warm equatorial waters along the western coast of Australia to higher latitudes. Therefore, ITF dynamics are a vital component of global thermohaline circulation. Plio-Pleistocene changes in ITF behavior and Leeuwin Current intensity remain poorly constrained due to a lack of sedimentary records from regions under its influence. Here, organic geochemical proxies are used to reconstruct sea surface temperatures on the northwest Australian shelf at IODP Site U1463, downstream of the ITF outlet and under the influence of the Leeuwin Current. Our records, based on TEX 86 and the long-chain diol index, provide insight into past ITF variability (3.5-1.5 Ma) and confirm that sea surface temperature exerted a control on Australian continental hydroclimate. A significant TEX 86 cooling of~5°C occurs within the mid-Pliocene Warm Period (3.3-3.1 Ma) suggesting that this interval was characterized by SST fluctuations at Site U1463. A major feature of both the TEX 86 and long-chain diol index records is a strong cooling from~1.7 to 1.5 Ma. We suggest that this event reflects a reduction in Leeuwin Current intensity due to a major step in ongoing ITF constriction, accompanied by a switch from South to North Pacific source waters entering the ITF inlet. Our new data suggest that an additional ITF constriction event may have occurred in the Pleistocene. Plain Language Summary The Indonesian Throughflow (ITF) represents warm water masses flowing from the western Pacific into the Indian Ocean. The ITF flows through the narrow marine passages of the Indonesian Archipelago. This Indonesian Gateway in turn limits the amount of water moving from the Pacific into the Indian Ocean. The depth and width of the Indonesian Gateway has decreased gradually over the past 5 million years due to tectonic movement, which has caused Indonesian islands such as New Guinea and Halmahera to grow and block water entering the Indonesian Archipelago from the warm South Pacific. As a result, most ITF water now derives from the cooler North Pacific, which impacts Indian Ocean temperatures and broader global ocean circulation and heat distribution. The timing of this shallowing of the Indonesian Gateway and transition from warmer South Pacific to cooler North Pacific ITF source waters is not yet fully understood. Here, we present a new sea surface temperature record from near the ITF outlet that shows intense cooling just after 1.7 million years ago. We suggest that this cooling occurred in response to a significant step in the ongoing tectonic constriction and shallowing of the Indonesian Gateway.

Plio‐Pleistocene Continental Hydroclimate and Indian Ocean Sea Surface Temperatures at the Southeast African Margin

“…Other reconstructions of past temperature using TEX 86 in the southwest Indian Ocean (e.g., Schefuß et al, 2011) similarly interpret an uppermost water column export signal. For comparison to Site U1478 SSTs, we use BAYSPAR calibrated TEX 86 values (Tierney & Tingley, 2014 from IODP Site U1463 (Smith et al, 2020) and from Deep Sea Drilling Project (DSDP) Site 231 (Liddy et al, 2016) ( Figure 1b). We additionally convert Mg/Ca ratios from planktonic foraminifera at ODP Site 763A (Karas et al, 2011) to SST, using the multispecies calibration provided by Anand et al (2003), for comparison to Site U1478.…”

“…The tectonically induced reorganization of the ITF likely occurred between 5 and 3 Ma, with many records from the eastern Indian Ocean suggesting a transition to cooler and less saline conditions linked to flow constriction and the switching of Pacific source waters sometime between 3.5 and 2.95 Ma (e.g., Karas et al, 2011). More recent studies that have extended into the Pleistocene provide evidence for later major steps in ITF constriction (Petrick et al, 2019;Smith et al, 2020). At Site U1478 we observe a significant, gradual ∼3°C SST decrease from ∼3.7 to 3.2 Ma that is synchronous and similar in magnitude to SST decreases at ODP Site 763A (Karas et al, 2011) that is proximal to the Indonesian Gateway, likely recording ITF variability (Figure 4).…”

Dating the Northwest Shelf of Australia Since the Pliocene

“…(a) Spectral analysis of the δ 13 C benthic record of IODP Site U1463 in the depth domain reveals significant cycles at ∼2.2 and ∼24 m; (b) Shipboard-based magneto-and biostratigraphy allow identification of 405-kyr eccentricity cycles and initial age model related to the orbital solution (Laskar et al, 2004). Black crosses indicate shipboard calcareous nannofossil and planktonic foraminiferal biostratigraphic age markers (Gallagher et al, 2017); (c) Correlation of the TEX 86 record (Smith et al, 2020) in the depth domain with the benthic δ 18 O-stack LR04 (Lisiecki & Raymo, 2005); (d) Correlation of the benthic δ 18 O in the depth domain with the benthic δ 18 O-stack LR04 (Lisiecki & Raymo, 2005). Gray, vertical lines between the records in panels b-d indicate tie-points; dark gray lines indicate tie-points based on the proxy in that particular panel.…”

“…Karatsolis et al (2020). Temperatures (Smith et al, 2020), and K (%) (Christensen et al, 2017;Karatsolis et al, 2020) of IODP Site U1463…”

The Novel Hydroxylated Tetraether Index RI‐OH′ as a Sea Surface Temperature Proxy for the 160‐45 ka BP Period Off the Iberian Margin

“…The Iberian Margin thus constitutes a much more favorable sedimentary setting to validate the novel RI-OH′ and RI-OH paleothermometers than the Gulf of Lions (Davtian et al, 2019). Contrary to Davtian et al (2019) and similarly to other multiproxy studies (e.g., Fietz et al, 2013Fietz et al, , 2016Fietz et al, , 2020de Bar et al, 2018de Bar et al, , 2019Jonas et al, 2017;Lattaud et al, 2018;Lopes dos Santos et al, 2013;Smith et al, 2020), we studied all organic proxies using a single set of lipid extracts to facilitate comparisons between novel and established paleothermometers. The deep sea study sites also offer an opportunity to assess whether, in the Iberian Margin, Mediterranean deepwater archeal communities bias RI-OH′ and RI-OH to the same extent as TEX 86 , a bias that is likely insignificant at the shallow sea study site of Davtian et al (2019).…”