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Abstract Intracellular calcium (Ca²⁺) is ubiquitous to cell signaling across biology. While existing fluorescent sensors and reporters can detect activated cells with elevated Ca²⁺levels, these approaches require implants to deliver light to deep tissue, precluding their noninvasive use in freely behaving animals. Here we engineered an enzyme-catalyzed approach that rapidly and biochemically tags cells with elevated Ca²⁺in vivo. Ca²⁺-activated split-TurboID (CaST) labels activated cells within 10 min with an exogenously delivered biotin molecule. The enzymatic signal increases with Ca²⁺concentration and biotin labeling time, demonstrating that CaST is a time-gated integrator of total Ca²⁺activity. Furthermore, the CaST readout can be performed immediately after activity labeling, in contrast to transcriptional reporters that require hours to produce signal. These capabilities allowed us to apply CaST to tag prefrontal cortex neurons activated by psilocybin, and to correlate the CaST signal with psilocybin-induced head-twitch responses in untethered mice. 

Abstract Ocean circulation supplies the surface ocean with the nutrients that fuel global ocean productivity. However, the mechanisms and rates of water and nutrient transport from the deep ocean to the upper ocean are poorly known. Here, we use the nitrogen isotopic composition of nitrate to place observational constraints on nutrient transport from the Southern Ocean surface into the global pycnocline (roughly the upper 1.2 km), as opposed to directly from the deep ocean. We estimate that 62 ± 5% of the pycnocline nitrate and phosphate originate from the Southern Ocean. Mixing, as opposed to advection, accounts for most of the gross nutrient input to the pycnocline. However, in net, mixing carries nutrients away from the pycnocline. Despite the quantitative dominance of mixing in the gross nutrient transport, the nutrient richness of the pycnocline relies on the large-scale advective flow, through which nutrient-rich water is converted to nutrient-poor surface water that eventually flows to the North Atlantic. 

Abstract Dissolved organic nitrogen (DON) is the dominant form of fixed nitrogen in most low and middle latitude ocean surface waters. Here, we report measurements of DON isotopic composition (δ¹⁵N) from the west South China Sea (SCS), with the goal of providing new insight into DON cycling. The concentration of DON in the surface ocean is correlated (r = 0.70,p < 0.0001) with chlorophyllaconcentration, indicating DON production in these surface waters. The concentration and δ¹⁵N of DON fall in a relatively narrow range in the surface ocean (4.6 ± 0.1 μM and 4.3 ± 0.2‰ vs. air, respectively; ±SD), similar to other ocean regions. The mean DON δ¹⁵N above 50 m (4.5 ± 0.3‰) is similar to the δ¹⁵N of nitrate in the “shallow subsurface” (i.e., immediately below the euphotic zone; 4.6 ± 0.2‰) but is higher than the δ¹⁵N of suspended particles in the surface ocean (~2.3‰). This set of isotopic relationships has been observed previously (e.g., in the oligotrophic North Atlantic and North Pacific) and can be explained by the cycling of N between particulate organic nitrogen (PON), DON, and ammonium, in which an isotope effect associated with DON degradation preferentially concentrates¹⁵N in DON. Consistent with this view, a negative correlation (r = 0.70) between the concentration and the δ¹⁵N of DON is observed in the upper 75 m, suggesting an isotope effect of ~4.9 ± 0.4‰ for DON degradation. Comparing the DON δ¹⁵N data from the SCS with other regions, we find that the δ¹⁵N difference between euphotic zone DON and shallow subsurface nitrate δ¹⁵N (Δδ¹⁵N_(DON‐NO3)) rises from ocean regions of inferred net DON production to regions of net DON consumption, with the SCS representing an intermediate case. 

Abstract. Marine diazotrophs convert dinitrogen (N2) gas intobioavailable nitrogen (N), supporting life in the global ocean. In 2012, thefirst version of the global oceanic diazotroph database (version 1) waspublished. Here, we present an updated version of the database (version 2),significantly increasing the number of in situ diazotrophic measurements from13 565 to 55 286. Data points for N2 fixation rates, diazotrophic cellabundance, and nifH gene copy abundance have increased by 184 %, 86 %, and809 %, respectively. Version 2 includes two new data sheets for the nifH genecopy abundance of non-cyanobacterial diazotrophs and cell-specific N2fixation rates. The measurements of N2 fixation rates approximatelyfollow a log-normal distribution in both version 1 and version 2. However,version 2 considerably extends both the left and right tails of thedistribution. Consequently, when estimating global oceanic N2 fixationrates using the geometric means of different ocean basins, version 1 andversion 2 yield similar rates (43–57 versus 45–63 Tg N yr−1; rangesbased on one geometric standard error). In contrast, when using arithmeticmeans, version 2 suggests a significantly higher rate of 223±30 Tg N yr−1 (mean ± standard error; same hereafter) compared to version 1(74±7 Tg N yr−1). Specifically, substantial rate increases areestimated for the South Pacific Ocean (88±23 versus 20±2 Tg N yr−1), primarily driven by measurements in the southwestern subtropics,and for the North Atlantic Ocean (40±9 versus 10±2 Tg N yr−1). Moreover, version 2 estimates the N2 fixation rate in theIndian Ocean to be 35±14 Tg N yr−1, which could not be estimatedusing version 1 due to limited data availability. Furthermore, a comparisonof N2 fixation rates obtained through different measurement methods atthe same months, locations, and depths reveals that the conventional15N2 bubble method yields lower rates in 69 % cases compared tothe new 15N2 dissolution method. This updated version of thedatabase can facilitate future studies in marine ecology andbiogeochemistry. The database is stored at the Figshare repository(https://doi.org/10.6084/m9.figshare.21677687; Shao etal., 2022).