Particulate phases transport trace metals (TM) and thereby exert a major control on TM distribution in the ocean. Particulate TMs can be classified by their origin as lithogenic (crustal material), biogenic (cellular), or authigenic (formed in situ), but distinguishing these fractions analytically in field samples is a challenge often addressed using operational definitions and assumptions. These different phases require accurate characterization because they have distinct roles in the biogeochemical iron cycle. Particles collected from the upper 2,000 m of the northwest subtropical Atlantic Ocean over four seasonal cruises throughout 2019 were digested with a chemical leach to operationally distinguish labile particulate material from refractory lithogenics. Direct measurements of cellular iron (Fe) were used to calculate the biogenic contribution to the labile Fe fraction, and any remaining labile material was defined as authigenic. Total particulate Fe (PFe) inventories varied <15% between seasons despite strong seasonality in dust inputs. Across seasons, the total PFe inventory (±1SD) was composed of 73 ± 13% lithogenic, 18 ± 7% authigenic, and 10 ± 8% biogenic Fe above the deep chlorophyll maximum (DCM), and 69 ± 8% lithogenic, 30 ± 8% authigenic, and 1.1 ± 0.5% biogenic Fe below the DCM. Data from three other ocean regions further reveal the importance of the authigenic fraction across broad productivity and Fe gradients, comprising ca. 20%–27% of total PFe. Plain Language Summary The availability of dissolved iron controls phytoplankton growth in much of the ocean. Most oceanic iron is contained in particles that are a mixture of live and dead cells (biogenics), crustal material (lithogenics), and minerals that have precipitated in seawater (authigenics). Each of these materials has different chemical properties that determine how iron cycles through the ocean and regulate how much iron is available for uptake by phytoplankton. Specifically, authigenic and biogenic forms are more accessible to phytoplankton but are often measured as one fraction despite formation by different processes. We measured different forms of iron in particles across seasons and environmental gradients and found that 20%–30% of iron is authigenic. Key Points Iron in phytoplankton accounts for <80% of chemically labile Fe and does not exceed 0.1 nM Biogenic Fe is a small and relatively invariant component of particulate Fe (PFe) pools, even across seasonal and regional gradients Authigenic Fe is a significant fraction of particulate Fe across seasons and productivity gradients