Heat flow and thermal regime in the Guaymas Basin, Gulf of California: Estimates of conductive and advective heat transport

Abstract

Heat flow is estimated at eight sites drilled int the Guaymas Basin, Gulf of California, during the International Ocean Discovery Program Expedition 385. The expedition sought to understand the thermal regime of the basin and heat transfer between off‐axis sills intruding the organic‐rich sediments of the Guaymas Basin, and the basin floor. The distinct sedimentation rates, active tectonics, and magmatism make the basin interesting for scientific discoveries. Results show that sedimentation corrected heat flow values range 119–221 mW/m2 in the basin and 257–1003 mW/m2 at the site of a young sill intrusion, denominated Ringvent. Thermal analysis shows that heat in the Guaymas Basin is being dissipated by conduction for plate ages >0.2 Ma, whereas younger plate ages are in a state of transient cooling by both conduction and advection. Drilling sites show that Ringvent is an active sill being cooled down slowly by circulating fluids with discharge velocities of 10–200 mm/yr. Possible recharge sites are located ca. 1 km away from the sill's border. Modelling of the heat output at Ringvent indicates a sill thickness of ca. 240 m. A simple order‐of‐magnitude model predicts that relatively small amounts of magma are needed to account for the elevated heat flow in non‐volcanic, sediment‐filled rifts like the central and northern Gulf of California in which heating of the upper crust is achieved via advection by sill emplacement and hydrothermal circulation. Multiple timescales of cooling control the crustal, chemical and biological evolution of the Guaymas Basin. Here, we recognize at least four timescales: the time interval between intrusions (ca. 103 yr), the thermal relaxation time of sills (ca. 104 yr), the characteristic cooling time of the sediments (ca. 105 yr), and the cooling of the entire crust at geologic timescales.

PCR-based survey of methane-cycling archaea in methane-soaked subsurface sediments of Guaymas Basin, Gulf of California

“…Sediment samples, DNA yields, and PCR results are summarized in Table 1. Two neighboring sites (U1545 and U1546) on the northwestern end of Guaymas Basin (Teske et al, 2021b,c) essentially differ by the presence of a massive, thermally equilibrated sill between 350 to 430 meters below seafloor (mbsf) at Site U1546 (Lizarralde et al, 2023). Two drilling sites (U1547, Regarding their in-situ temperature gradients, the Guaymas Basin drilling sites fall into two categories, the hot Ringvent sites with steep temperature gradients of ca.…”

“…PCR-amplified mcrA genes were obtained from nearly all drilling sites of IODP Expedition 385 (Fig. 1) which differ in their degree of hydrothermally driven heat flow [30], and in the relative extent of marine vs. terrestrial sedimentation [31]. Samples yielding PCR amplicons were generally affiliated with subsurface maxima or with broad zones of high alkalinity and DIC concentration [32], a proxy for microbial organic matter remineralization (Supplementary Figures S1a-h and S2).…”

“…These cracks lead to temperature measurements of diminished quality. For a detailed protocol of the downhole temperature measurements, refer to Section 3.2 in Neumann et al, 2023. Temperature values were interpolated for each sample using linear regression of the local thermal gradient (°C/m) multiplied by depth (mbsf), plus the y-axis intercept: U1545A,B, T = 0.225 x depth + 4.899; U1546A, T = 0.221 x depth + 2.627; U1547A/B, T = 0.511 x depth + 13.01; U1548A, T = 0.646 x depth + 8.301; U1548B, T = 0.804 x depth + 6.5; U1548C, T = 0.958 x depth + 15.916; U1548D/E, T = 0.271 x depth + 3.241; U1549A, T = 0.194 x depth + 3.228, U1550A, T = 0.135 x depth + 3.532; U1551A, T = 0.1 x depth + 4.741; U1552A/B, T = 0.262 x depth + 3.543.…”

The DNA event horizon in the Guaymas Basin subsurface biosphere: technical advances and re-defined limits in bulk extractions of nucleic acids from deep marine sediments

“…Cultivation-independent sequencing studies of microbial communities in the deep subsurface require extraction of nucleic acids in sufficient quantity and quality for subsequent high-throughput sequencing. Here we examine the outcome of DNA and RNA extractions for deep subsurface sediments from Guaymas Basin, a sedimented, hydrothermally active spreading center with steep thermal gradients and high heat flow in the axial troughs and flanking regions (Neumann et al, 2023). We focus on Guaymas Basin sediments because among deep-sea sediments they are some of the most challenging sediments to extract nucleic acids from due to their high content of organic material, including hydrocarbons that can interfere with the activities of enzymes and other reagents in extraction protocols.…”

“…Drilling Site U1549 (Teske et al, 2021e) explores the periphery of an off-axis methane cold seep, Octopus Mound, located ~9.5 km northwest of the northern axial graben (Teske et al, 2021f). Of all these sites, the two Ringvent sites have the steepest thermal gradients (between 506 and 958°C per km) and the highest heatflow values (between 516 and 929 mW per m 2 ) (Neumann et al, 2023). This distinct thermal regime is caused by a recently emplaced, shallow volcanic sill that is driving local hydrothermal circulation (Teske et al, 2019).…”